I agree the UI is a little wild but definitely give retroarch a fair shot. Once you understand how it all hangs together it's an awesome platform. Drawing together all those other projects into one is a wicked idea.
Concerning PSVita native emulation : pFBA emulate some console and arcade systems. Genesis Plus GX, SMSPlus and Snes9x are having a standalone VPK too.
To conclude, I think about ScummVM one of my favourite emulator ^^
Maybe there's more...
If you add PSP emulation there's a way more possibilities. (Emulating NeoGeo CD using NDZPSP for example).