I love a challenge but I fear that the economics just aren't going to make this one work out.
I'm going to make a number of assumptions:
- You live near BHX and would rather travel from there if possible
- The appeal of travel to/from LHR is the Clubhouse in UC
- Mrs Subman will permit creative routing provided we can justify it
- You have no status with any airline (so we have a free hand in picking which to use
- The aim of the trip is to get to LAS and mentions of East Coast destinations were just to connect and not another place to visit on the trip
- Your dates are flexible in September
Is your £500 return BHX - LAS with AA?
If so I think it's this:
http://goo.gl/flights/D5Y1
The AA option will generate 2* (845 + 562) = 2814 Avios for your household account, in other words, not a lot.
You can also do a 2-stop for £415 each
http://goo.gl/flights/rD0V
It's not as mad as you might think because you actually arrive before the 1-stop route and get a teeny bit more legroom on the long leg and leaves you £170 more to play with in LAS.
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If we look at Oneworld I think you can get:
BAEC 5k + Avios 3k + SPG 11k + Heathrow Rewards 5k = 24k avios. You don't want to covert your Carlson or IHG points because of the terrible exchange rate and you will also miss out the 5K bonus for converting 20k SPG by doing this.
Booking LHR - LAS with BA is £823 in economy (ouch, that's the same cost for one person as the indirect route for BOTH of you) and 16,250 avios each to upgrade to WTP one way. So you don't actually have enough avios to do this for both of you and I can't find any availability anyway
The economy price makes no sense when you can fly PE both ways for £1,029
http://goo.gl/flights/AC1U
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On Virgin you have 60k and a potential for 60k + SPG 11k + Heathrow Rewards 5k = 76k (I'm ignoring the all miles from one account just for the minute)
The cheapest fare that will allow a 1-way upgrade is £857 (X outbound, O inbound) with 22,500 miles each to upgrade to PE or 40,000 each to upgrade to UC.
Considering the significantly higher base fare I can only see this being worthwhile if you can manage to earn some additional miles and do PE in both directions (90k needed) or blow it on UC outbound (80k needed). A single PE leg just doesn't justify the total spend that would be involved.
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Edit: I notice playing around on Air France's site you can book the BHX - AMS - SLC - LAS outbound in Y and LAS - DTW - CDG - BHX return with all legs in PE for £880 each.