I'm not going to jump on the anti PSP band wagon here, since I've probably played it far more than i ever played my DS, which apart from pearl and Rocket Slime, i found was insanely boring.
However, I wouldn't let anybody's negative opinion(s) iinfluence your decision, as your taste in games is probably very different to theirs.
I think however, you should disregard a lot of the anti PSP messages here, this is after all a Pokemon forum, full of Nintendo fans. Most of the people here who slam the PSP probably haven't and won't ever play/ed one. I'm going to try and be as objective and fair as possible in this post, which is kind of hard with bias comments such as "PSP SUX BALZ"
Anyway, you've already had a DS, did you only really use it for Pokemon Emerald/Fire Red? If so, is it really worth rebuying a console to play just 2 games? Maybe it would be cheaper to buy a preowned GBA SP?
If you're still considering getting a PSP then you should understand that although it has some really good games, it has many more awful ones (As does the DS actually) so it may be a bit touch and go with weather you'll enjoy the games. There's Monster Hunter, which is somewhat similar to pokemon, there's also a bulk of RPGs (Some old, some new) which are pretty enjoyable. What is most noteworthy is the bulk of content coming out soon with the release of Sony's PSPgo. There's a Fat princess game coming, a Metal gear Solid (which looks amazing) a portable LittleBigPlanet, a Gran Turismo, a new Jak and Daxtar game etc etc. PSP also has a hefty back catalog of downloadable PS1 titles and a few PSN games. (The number of these will greatly expand when the PSPGo is released) Also, although i wouldn't advise you take this route, you can hack a PSP pretty easily to play GBA roms (Again this is piracy, so i wouldn't do it, just a testament of what the system can do with a little tinkering) It also has WiFi, can play most audio files, will play .Avi, .wmv and .MPEG4 video files and also has Skype.
edit Just saw your post, guess my post was kind of pointless then haha.