What's that additional 20K EQM going to get you on AA? There is a small difference between PLT& PLT Pro (I don't think the cards exempt the $6-9K EQDs on AA?)... You would definitely miss a lot of free upgrades as UA Gold, but you'd consistently get an economy plus seat - I guess you could always pay to upgrade. Scheduling is probably the biggest argument for UA on your list. If you have the United Club Card, you don't have to be flying United to use the lounges, BTW... Although T3 at SFO doesn't connect to T2 airside...
You could devote all that spending to a card that has a more diverse portfolio of redemption options and value (Amex Plat or CSR) and use that to redeem *A awards or whatever you'd like. Just tossing around ideas here.