1. Yes, I think there is still work being done on the ScummVM port but don't expect/demand a release soon the coder/coders (not sure if DJW ended up with help yet...) wants to make it the best possible release he can before distributing it and if you think about that it's a good thing

Eventually the GP32 version will get a nice release that will work incredibly with both OGG and MP3 (atleast that's my hope but I'm not really a coder so I can't actually tell ya)
2. DJWillis has released a binary of version 0.5.1
here I suggest you skip using the ogg support for the newer games for now (ie. DOTT and Sam & Max) and use the floppy version monster.sou file so it'll fit on the SMC and you can listen to the sound effects and a little talking... Loom seems to run quite well with OGG music though.
3. SNES Emulation is nice on the GP32 (but that's my opinion) it's a little slow and somethings are not supported yet. There's two emu's OSNES9XGP which is open source and still has the potential for improvement and SNES9XGP which has transarencies and if OC'd to 166Mhz is pretty good also. If your looking for fullspeed with no frameskip and full sound and game support (ie. any superFX games, SDD1 games don't work right now either as far as I know and maybe a couple others) but is generally pretty decent and most people are willing to enjoy it as is (my friends literally steal my GP32 from me if they hear Super Mario World playing and seem to enjoy themselves) sometimes with OSNES9XGP you have to mess with the settings to get certain games to work (I personally use SNES9X clocked to 166Mhz for playing Super Metroid, but otherwise use OSNES9XGP for most games) it's enjoyable but just try and play SNES on an emulator on a 133 or 166Mhz pentium and you'll get the idea...(no it's not an equivalent there's alot of differences between these two platforms) actually I think the pentium will be slower but can't remember.
And also remember there's also a load of PC fps ports (like ROTT, Wolf3D, Heretic(which I never got to work...) and Doom... right now Doom is THE most complete of the fps listed and is great on the GP32) and there's other emu's and lots of freeware games and utilities, ect. I've been happy with my GP32 since I got it and can't wait to see what get's released next. If you like Sonic or any Genesis Game I think you'll be happy to see the new release of fGen32 or even GigaDrive (which is a little different in handling the sound for now) but both have potential to turn into great Genesis emulators just remember that they don't have z80 sound implemented...yet! There is also a port of Sarien which runs those old Sierra games
So in other words, I'm pretty sure you'll find atleast ONE thing that you will like on GP32 that is total freeware (and I haven't even mentioned the Movie Player or MP3/WMA/OGG players or anything like that) but I have to admit some of the commercial games are quite iffy in some cases... but if you like lemmings there's a great commercial game made by one of the homebrew dev's from the community and only costs $5 US.
I'm a horrible self promoter for this but you may want to look at the very bottom of my post, go to my webiste and read my interviews (I apologise if you don't like the frontpage but it's better than the one I made originally) it'll give you a good idea of what the future of the GP32 has in store
Have a good day!