Hi there, I live in Asia and need to switch from Delta to a program that benefits my travel both to the US and to Africa, which seems to be Star Alliance for code share with SQ and SAA

Home Airport: SIN
Fly per year: 25-50K majority international
Most common routes: SIN-NRT-SFO/LAX or SIN-JNB/CPT

I used to enjoy flying EK through DXB, but added a baby so the non-stop SIN-JNB is preferred now. I am Gold Status on Delta and Silver on EK. I tend to fly SIN-NRT-SFO for work with a econ ticket that is upgradeable with miles, and EK to South Africa but that is almost double the time SIN-DXB-CPT.

My question:
I'm considering joining US Airways b/c I can fly on SQ metal to the US and South Africa, and rack miles using the credit card. However, it gets complicated - the SAA tickets are significantly cheaper than the SQ tickets on the same metal - so question -can you upgrade on SAA ticket on SQ metal using the US Airways miles b/c of StarAlliance? Similarly, can you upgrade on a US Airways ticket flying SIN-SFO/LAX on SQ metal (code share)?

Most important to me:
Upgrades using miles earned. Award tickets.

Thanks for any advice you might have.