Saw a car yesterday that made me think about this thread - it was a tricked out Scion tC. I'm sure some will take this the wrong way, but no matter how much you dress up a 370Z it will never be a GT-R. If you've got the cash for a GT-R, I think that's what you should get - it's the real deal fo' shizzle.
The question really boils down to how much time you want to spend mod'ing the 370Z versus just driving the GT-R. The choice is yours but I know what I would do.