Originally Posted by SchmutzigMSP

1. I wouldn't necessarily count on a match to Plat, even if you're EXP on AA. Generally, AFAIK, most airlines won't match top-tier to top-tier. But you can always ask for a straight-up match. And if they only offer Gold, ask for a Platinum challenge (i.e. fly X number of flights in Y days in some fare class or something like that).
2. As mentioned, there are elite extraperks. There are also NW AnyFare upgrades floating around. I think those are awarded through the BizPerks program and you might have to trade for those. Short of those, I think mileage upgrades are the best routes, and right now, you can only upgrade trans-Atlantic and trans-Pacific itineraries on eligible paid Northwest Y and B type fares, Continental Y and H type fares, and on KLM S and B type fares.
3. I don't know, but generally on a flight like that, I think CO is going to have a lot of its own Plats. Plus, CO generally has fewer seats in FC on the same aircraft type as NW. Although, they do have 7 (7?!) flights daily between LAX-EWR, so maybe you'd have a shot?

If you're going to be flying CO a lot, it may be worth considering a match over to CO. What is it about earning in WorldPerks but flying CO that you like?