A Nismo is a series of overpriced parts... who cares??? do what you want. Nobody will be saying 10 years from now that the Nismo was any better than sport pkg base/touring cars. Intake,hfc exhaust and tune on a reg Z will net you a 50hp. for $2600. $1200 in suspension parts will kill all that makes a nismo suspension anything worth talking about.
The body kit is the only truely nice thing about a Nismo, but it's more rare to have a Amuse or Fujimura kit...
Do what you want. Nismo has no value over time over any other Z, unless badges really become that meaningful in this country over time???