Concierge isn't worth it at all unless you a serious Trans Atlantic flyer, companion tickets and the vouchers really are worth it then. I had a colleague who did DUB-ORD-SEA monthly in Gold Circle days, that was worth ~12000 in old program money (UA were quite generous) so easily got the card and in those days you could phone up and get any seat you wanted assigned.

Platinum is a good sweet spot, you still can guest in (and use the SFO lounge), you get 1 upgrade voucher, get the strange LHR benefits

Only thing you miss out really is the change fee wavier, if I'm flying for work thats works problem, I've only changed my personal plans once in living memory (thanks Covid diagnosis)