You're honestly not going to get much better as a 50k/yr flyer. None of the carriers, AFAIK, offer international upgrade instruments. UA will let you use miles + copay from any of their fares, but now it's harder to get miles, and they're tightening up on upgrade space.

I'd probably go to OW, since PHL is a US hub (and I've found OW to price better than *A out of PHL), SFO could be reached via AA/US, FRA can be reached with a single connect via LHR or a double connect via TXL, SIN can be reached...I dunno, via HKG? The south, especially the SE (heh), tends to be best-served by OW, iirc.

I'd personally suggest doing a US Airways challenge for some status of your choice ($200 for 90 days of Silver, $400 for 90 days of something higher, $600 for 90 days of a step above "something higher") and then fly 30k within 90 days to get US CP (equivalent to SE). That'll then convert to AA EXP, giving you 10 AA SWUs, in Q2 2015, and you'll fall down to AA Gold (30k miles flown in a year) Feb 2016.

Having said that, I'm pretty sure there was another consolidated thread on status matches that this thread would fit well in.