I did a little more googling, and would like some clarification:

The Carte Mobilis:

The 3 day Z1-3 Paris Visit Pass is 23,40 €. Will this work on the train to/from Asnieres-sur-Seine? I am not getting train travel clearly defined on most of the googled websites I am reading about tickets/passes, so I am very unsure...It is claimed that RATP and SNCF trains are covered by this pass...

The daily rate of the Carte Mobilis is 8,8€ (26.4€ for 3 days). So the Paris Visit Pass (3 days, zone 1-3) is a better deal for me? Also, I plan on going up to the Arc de Triomphe, so the discount helps a little.

One ticket will do you - I can't find the fare right now, I'm afraid, but it's similar or same as the fare from central Paris. Downside is that it's a slightly annoying route, with two convoluted changes. It may be easier to use the Roissybus shuttle to/from rue Scribe, and walk the 5-10 minutes to St Lazare from there, depending on your luggage and the time of day.

And yes, if it's 3 days then the Paris Visite is a good deal. The RATP site isn't clear, but if you dig into the detail, it is accepted on Transilien SNCF services, not just RER SNCF services, so you would be OK to Asnieres.

I am back. I want to confirm/answer some of the questions I asked, and then ask another one...

Yes, the Mobilis and the Visite Paris pass both worked well on the Transilien/SNCF train. It was explained clearly in the literatures and ticket sale machines in Paris.

The Mobilis 2-zone pass was €6.6 per day and 3-zone was €8.8.
The Visite Paris pass for 3-zone for 3 days was €23.4

I ended up buying the 3-zone Visite Paris pass for €23.4 cuz it was cheaper than the 3 days of Mobilis pass and I wanted to visit the Montparnasse tower (30% discount = €3.5 off) and Arche de triomphe (20% off = ~€2), so it was by far the better deal.
Also, as expected, I was dead tired by the time I got to Paris, and the weather wasn't perfect, so I rode on various buses almost all 3 days I was there. That was pretty fun too.

(I may be off by a few tenths of Euro in some of the prices above).

Question: I learned (the hard way!) that the visite Paris pass expires at/near midnight. On my last night, I stayed at the Grand Arche (La Defence) too late, taking photos, and was denied getting on the subway. I ended up having to buy tickets. The price for individual tickets were €2.7, while 10 was €20.xx. The next day, I asked the lady at the subway, but she was not able to explain to me the significance or difference of these tickets from La Defence. Why are they so much more expensive compared to individual/carnets at regular Paris subway ticket machines? Do they have special usage I can take advantage of? (in hindsight, I should of brought only 1 instead of 10....)

One interesting tangental story: I not only lost usage of my Visite Paris pass to get back to my hotel beside Asnieres-sur-Seine train station, I missed the last train from St. Lazare. I know there is an ~hourly night bus, but I literally missed it by 15 seconds at St. Lazare station. Not wanting to wait another hour or so (it was 1:20am by then), I decided to take the subway to Gabriel Peri and jog the 1.2km to my hotel. Of course, with my luck, when I got to the station exit, google map on my phone didn't work for some reason, and I have no idea how to get to my hotel. But luckily, after trying to explain my situation to a bunch of RATP employees, and trying desperately to get them to at least point me in the direction of the train station, one of them stylishly tossed his cigarette, pointed at his company car and then drove me to my hotel!

Another unrelated note: MacDonald Cafe Macaroons in Paris are quite good, especially considering their price! (I brought a dozen for €10.) Much much better than the free ones at the Air France Lounge at Terminal 2e. :-)

La Defense station is in a weird situation. The RER/SNCF is in zone 3, so is outside the central Paris ticketing area, hence te extra cost. However, the metro part of the station is considered to be in zone 2, because it's the metro. If you want to buy a "ticket t+" carnet, as opposed to the more expensive z3-z1 one, you have to go to the metro part of the station.

Sounds like you had a great trip, though!

No, it does not: its validity starts at 05.30 and ends at 5.30 on the next day. At least, this is according to RATP site.

http://www.ratp.fr/fr/ratp/c_22599/paris-visite/

I quote:
Paris Visite est un forfait valable 1, 2, 3 ou 5 jours consécutifs sur les zones 1 ŕ 3 ou 1 ŕ 5 (Attention: la journée commence ŕ 5h30 et se termine ŕ 5h30 le lendemain).

Hmmm, the pass was working great all day saturday, until I tried getting through the SNCF gate at La Defence. I then tried the ticket at the other side - the Metro station side, and it didn't work either.

Perhaps I somehow invalidated the ticket by putting it through the SNCF ticket gate?

This was some time between 12:30am (technically sunday) and 1am.

I did have a great trip!

So, I have these white tickets with the M, RER, and SNCF logos on it (no "t"). Also printed on it "La Defence". So can I use these tickets for something extra that the regular "t" tickets can't do? Or are the tickets the same, but simply cost more because of where I brought them? Also, I first tried buying the tickets at the SNCF ticket machines, which gave me the initial sticker shock of 2.7 for 1 ticket and 20.x for 10. Then I walked ~50 feet toward the METRO side and got quoted the same price on the older RATP machines with the big rolling pin.

Hmm, I'd say it shouldn've been, but you could've triggered their 'time restriction' system (there is a time limit imposed on each 'period' ticket, meaning such a ticket, once used, can only be used next time in 10 or so minutes, so to prevent it from been used by more than one person). RER and Metro are two different systems and theoretically no such restriction should exist in your case, but who knows...

P.S. RER line A is not SNCF, it's managed by RATP, as is metro. I presume you tried to get access to the RER station...

I arrived at La Defence via METRO shortly after midnight. Spent 15 minutes walking around the Arche, then tried to get in the train station. (I previously looked at a train map and believe there is a train that goes from La Defence to St. Lazare, passing through my stop) I believe it was the SNCF (Transillian) gate, but it may be the RER gate...maybe they were the same gate? Anyway, I put the ticket it, and I heard a buzz, and the gate didn't open. So I tried again, and it did the same thing, with a red stop sign lighting up. I walked over to the Metro gate and it gave the same red stop sign... People were hopping over the gates left and right at that point, and I was temped to do the same (but did not). So I went and brought Euro 20 worth of tickets.... I did not think of the system having some sort of double-usage prevention.... I threw the ticket away thinking I was wrong about the expiration time of my VISITE Paris pass... Oh well, a Euro 20 mistake.

Was purchasing the tickets an issue without a chip and pin CC?

Also if I am staying at the Marriott Champs Elysees will I need to take the subway to a lot of the tourist attractions (Louve, Seine, Eifel Tower, etc.).
Should I wait until I get there or is there an advantage to buying a head of time?

I have purchased a 3 day museum pass as an FYI.

I have a chipped credit card, and I brought my 3-day VISITE PARIS pass from a metro ticket agent (a person), so I can't answer your initial question.

I see no good reason to buy the museum pass ahead of time. As far as I can tell, most of those museums will sell you the pass the same way you buy the regular admission ticket. I did find that getting in some of the places faster with the pass. I brought mine when visiting Versailles. Another reason is: If for whatever reason (sickness, energy, weather), one of your party doesn't want to visit all those places, then you wasted your money.

Walking between the sights: It really depends on your ability and interest in hiking. I've walked a lot in past Paris trips (and this one), but for most tourist, walking from, for example, the Eifel tower to any of the other big tourist attraction is far. i would recommend instead to use the subway to conserve energy and time. If you get a 2 zone day pass for Euro6.6, you don't have to worry about transit cost and just take the fairly simply subway system to where ever you need to go. If you are visiting in the summer, Paris is humid (compared to Portland), so you will get sweaty.

Regarding your museum pass: Are you sure you have a 3 day pass? I think they only sell 2 and 4 and 6 day passes... You must visit Palace of Versailles to make it worthwhile to get your money's worth, since it is by far the most expensive ticket on the list. Other must see places on the museum pass (my opinion of course):
Arc du Triomphe - the view up top at night is very nice
Tower of Notre Dame - the view up top is also very nice. long line up, and the pass doesn't help.... so go early!
Pantheon - Impressive building inside and out.
Orsay Museum - Not counting the art, I think this museum is the prettiest of them all...but no camera allowed!

There are so many other museums on the Pass, and you should pick the ones that really interest you. I am not the biggest art or museum fan, but I walked through most of them on my previous Paris trip and found them to be satisfying just to see the inside of the building. Most are in the central tourist area.

Thanks for the advice. I lived for 30 years in Houston, TX so humidity is not too big of an issue.

Meant 2 day pass and it was the Paris City Passport. Was linked on another thread and will be at the hotel waiting on us.

For 9 days, it would probably be easier to buy a zone 1-2 Navigo for one week (around 21EUR each, if I remember correctly + a one-time 5EUR for the card itself) and then a carnet for the extra two days. That would cost you about the same but gives increased convenience. Might even be a few EUR cheaper.

You are going to want to take the subway (and I also suggest using buses) to get around Paris. It would take most of an hour to walk from the Arc to the Louvre, longer to the Musee d'Orsay. Paris is a great walking city but public transport is too good and relatively too inexpensive to waste valuable time walking from one place to another.