Oh you can certainly compare them. The GP32 could do a vast ammount of bits and pieces - some of which the GP2x still can't (simply because the programs - typically emulators - haven't yet been released).
However, the 2x also has NeoGeo, better mame (iirc - though haven't been keeping track of the 32 releases), Amiga (not perfect, but better than none), an even better version of Castaway, a techdemo (but hopefully soonish more than that) psx emu, faster SNES emulation, and a load more.
It also takes cards that are big enough to store more than one film on at higher quality, and take enough music to actually turn it into a viable MP3 player (I considered the GP32's 128mb limit to be too low for that, given the price of cards - much more worth using it on games or a single movie; 1gb is a different story though).
So there is stuff the 2x can do that the 32 can't. However, equally, those who say the 2x wipes the floor with the GP32 should, if you've got access to one, go back to the older console for a while and remind youselves just how polished those games and emus actually are. I was playing DrMD side by side with the 2x and a GP32 OCed to 166MHz, and it was next to impossible to tell the difference between the experience. Except the GP32 had that wonderful (if overly clicky) stick which actually might have meant it was playing better!