With the Stable build, I think it's safe to say that it won't get much better, RetroArch wise. Which is fine, RetroArch wasn't really meant to optimize emulators for new platforms but rather make something easily portable and unified.
For those too lazy on o3DS to figure out which emulators are usable, here's what I use:
RetroArch's gpSP for GBA (not perfect but some games run fullspeed)
RetroArch's PicoDrive for Genesis/MD
GameYob for GB/GBC (audio isn't perfect but everything runs fullspeed)
blargSnes for SNES (not all games run on it, but the ones that run run well)
As for NES and most of your other 8bit stuff, I haven't really messed with them but I imagine it can't be hard to find ones that run well.
Honestly, this turned out better than I thought in such a short amount of time. I know it's not done, but thank you so much so far for your work
aliaspider and the folks at Libretro.