Have fun with that GTR!
I figure I would be brave and jump in for we non-boosted n00bs
My recommendation is to spend that money on the GTR. If not for performance, spend it on dress up so you feel that much more like a million bucks every time you get behind the wheel.
The only way I (personally) would go boosted if I was selling my Z in 2-yr time frame, is if I had a SERIOUS passion to do some boosted tuning, track racing, show-car appearances, project car for a magazine, etc.