I was going to buy a GP32 ages ago but I figured I would get get a GBA and Flash Cart.
Iv got to say I really only bought the GBA because of the software there are some great ports of games for example:The Pac Man Collection , Puyo Puyo , The Famicom Collect and so on and so on.
Not to mention that emulators are coming out for the SNES , and theres already ones out for the Game Gear and the NES.
I seen the plus points for the GP32 , but im happy not spending money on the roms all the time as well as batterys.
I think both systems are totally different and the only draw back of the GBA is its power and its screen size(its really tiny)
Well thats my two cents.