It seems like you are going through what I experienced about two years ago when I bought my NUR. It is extremely hard to keep the car stock, beacuse there is so much untapped potential in the engine. With the right tuner, the NUR engine is capable of 300+ RWKw easily with minimal modifications - Power FC, Cam gears, decat, free flowing exhaust, strengthened turbo actuators.
However, to be honest, I wished I had saved the extra dough I forked out for the NUR and gone for a VSpec II. The N1 based engine is not that much better than the normal RB!