I tried to sell mine not too long ago and it's nearly IMPOSSIBLE to sell a PSP Go used. I traded in a PSP 3000 at GS and I was able to get $110 in trade in credit toward another system but I have no idea what the PSP Go trades in for. Good luck, man!
It's too bad, too. It's a great little system but they really need to update the PSN games on the store or give an incentive to buy the digital version aside from saving on tax. There's barely anything there. Also, if you were able to play backups of your official games on it (NOT pirating!!) then you would probably see the PSP Go flying off the shelves. I'd love to be able to play a bunch of games that I own but aren't even offered on the PSN store.