My wife's 60th is coming up and we'd like to fly to London (from Denver, CO). My physical limitations require business class. Is it best to buy cheapest ticket, then upgrade using American Express points?
Assuming you are a member of the Membership Rewards program, and assuming that you wish to travel to London, UK:
I have found that one of the most lucrative ways to use American Express points is to transfer them to ANA's membership rewards program (which you can do one-to-one for free). ANA's program allows you to purchase any Star Alliance flight, and I have found that they have some of the best availability and pricing. For example, most round-trip trans-continental flights originating from the US are 68k points per person for business class, which is an excellent deal. If you don't quite have enough points to get your desired number of tickets, AmEx will even loan you some points that you will have to re-accrue within the next year (or else you pay a penalty). The downsides are that: