Entirely different marketplace. US airlines have historically run clubs, not lounges, in the US locations, sold memberships etc etc. They set planes up with premium seating rather than having flex cabins like European airlines do, so SFO-LAX will have typically a minimum 9 to 16 F seats, plus other elites, at one flight an hour etc etc. Too many people in the clubs for free. Instead, it is a nice profit center, collecting membership dues from road warriors. The model is changing some, but won't ever change completely IMO.

You can call AA to upfare your ticket. Just a shade over 2000 miles, IIRC, so you'll get a nice TP bump there. Price difference is likely to be 200 to 300 dollars each at a minimum, I would jump at 200, much higher than that and it starts to depend on TP need.

I did a RTW for a similar occasion and I can heartily recommend the experience Have fun.