Had a 97 GTP, loved the car, but the previous owner beat the hell out of it (common theme) and I was never able to get the problems worked out of it, even after a full engine rebuild and a heads & up rebuild. Probably should have gone with a race shortblock the first time around, but live and learn.
That said, I like my 00 Bonneville more for comfort, seats aren't as hard, but I wish I had my heated seats, moonroof, and HUD...not to mention I miss having a somewhat built L67. It isn't as sexy, but it'* nice to have a reliable car that'* invisible to cops to drive.
I want to get another GTP again in the future and build it bottom up right, but that'* probably a ways off. Make sure whatever one you get isn't beat, check out www.ClubGP.com
and read up on them first, but they are pretty reliable especially if you get one that'* a 1999-2002...the 97 had different features as it was an early model year, GM started getting cheap and replacing lights with reflectors, etc in 2002, and 2003'* had a somewhat different setup to get ready for the new models in 04.
I do miss the power of my GTP, and still wish that it had worked right after this summer'* rebuild because I did like that car. I just picked a cursed one. Your best bet though is to spend some time on ClubGP and research and price them.