I don't know when was the last time you tried emulation on your PSP but GBA emulation is quite fine and many other emulators works fine too. I suggest you revisit the hombrew catalog of PSP and come back after you really know its extend, nothing you can call a "mess" or "80% complete"...
I'm sorry if I came across too harsh, however
when it comes to emulators I'm really picky,
it's either 100% (sound & gfx) or it's a fail
I think the last time I checked the emulation stuff
on PSP was arround Xmas 2011
I tried some Star Wars SNES game and got like 15 FPS,
I also checked Castlevania (GBA) and got stuttering sound,
the last thing before I gave up in disappointment
was an Amiga emulator which lagged horrible.
I think the PSP (especially the little Go) is an excellent
device for PS1 and native games, for emulation not so much.
I fear the 3DS would be even worse in this department
cause it says 266 MHZ in the specs.
(I doesn't count that it is dual core and has special DSPs
as you will likely have no SDK to make use of all that.)
Afaik, neimod knows how to decrypt saves files and edit those to cheat, so there's no need of a Gateway to do such...
savegames? I think it's way cooler to install TSRs
and patch memory in realtime for fun.
They should also parse the Action Replay format XML files,
so we don't need to find all memory locations ourselves.