when you mod it forget about warranty
U r wrong... U can easily remove the traces of mod n claim warranty, even if u give them modded psp they wont object BUT they always return u the console with the latest firmware(not a big issue as mod for almost every FW is out now), but the main problem these dayz is that they return ur console with totally new mobo, is psp's lingo known as 9g mobo... This mobo can give some problem if not handled with care. So all in all try to keep ur console safe so that u never need to claim warranty, cause sony screws u when u give them ur console.
Source: i myself do mod consoles n have come around many psp owners screwed by sony when they claimed warranty.
@op try not to go for new console cause many of the new ones come with 9g mobo i'm talking about. They are easy to brick than the earlier mobos.
I will sell my psp 3004 too but i waiting for vita to launch in india.