Your Z is a sophisticated vehicle with computer control over engine performance. Without re-tuning the engine parameters using a system like UpRev's Osiris, the engine management will always be seeking to return the increased fuel or airflow to pre-programmed levels. If your NISMO 350Z is a genuine model (with V3 bodykit, welded body, numbered plate, etc), you are risking de-valuing it by modding it further. In addition, if your state or area requires emissions testing, a test pipe will not allow if to pass. Even if it doesn't any sale to a future buyer many be complicated b/c their state may require such testing.
My advise is to enjoy the NISMO Z as it is. Nissan designed it to be a well-balanced and reliable vehicle, but any changes you make will likely degrade it and activate check engine lights (CELs). Why not spend some money to make yourself a better driver? There are driving schools available that will help you to better exploit the performance of your Z.