dont do anything, in my experience weight reduction is the most worthless thing u can do to ur car. If you do anything at all just take out the spare tire, dont do anything more then that, i think for a 300zx, nissan claims 1/10 of a second of the quarter mile for every 150 pounds (this may be wrong), meaning that if u ripped out all of ur interior u would possible get alittle more then that gain, something that u can easily get from being a good shifter

 

you can also take a 1" drill bit and hollow out the inside door panels (The metal under the plastic cover). I dunno with everything I plan on doing I'm going to tear out my interior anyways to try to even the weight out.