Yes, it's very tempting to start making little mods here and there, but it's a bottomless pit once you start! Ive done and am doing a few to my R33 GTS-T, however, to be honest if I had a GTR I wouldn't touch the motor/turbo etc. They came from the factory w/ more then enough for your average driver and ability to use on public roads.
I would have to upgrade the alloys though to at least 18" and after market springs - just so the wheels fill out the arches!
Enjoy your machine mate