This coming from someone that has gone FI and hindsight is always 20/20. For those of you looking to begin modding, want big gains but without the headaches (and price tag) of a turbo kit.. these are the modifications I would go for and why. (This is on a 6mt Coupe by the way)
Tilton Street Clutch/Flywheel assembly - Believe it or not my car was just as fun with the Tilton as it is with the APS Twin Turbo.. if you can deal with the cement mixer noise (just get the idle bumped up to get rid of the noise) the revs were nothing less than beautiful.. and the gains were unbelievable. The dyno only showed 10hp but the fun factor felt like 30whp.. no joke.
3.9 Final Drive - Never had the chance to get this installed but from what I've read from other owners experience that it only enhances the Tilton assembly and it is another modification that may not show on the dyno but makes a big difference in performance..
Nismo Exhaust - Some people may not like how loud it is and if not then I say go with the fujitsu which is the same thing.. just quieter. I think the Nismo is just right as far as gains and aggressiveness goes, plus its lighter than stock so you just cannot go wrong.
High Flow Cats - I had Random Technologies but I do not recommend them, the gains were nice and they sounded great but they have a problem with collapsing, I hear crawfords high flow cats work nicely.
Injen Intake - I personally saw at a dyno day with 10-12 350Z and G35's, the ones with Injen Intakes consistently dyno'd higher than others with the Pop Charger, and Nismo intake.
Technosquare Reflash - Brings everything together and works nicely BUT... Utec will be releasing their product for G35's and 350Z's soon which will give you more options as far as tuning goes.
Everything else would be for ride/handling.. Nismo Sways or Hotchkis, Eibach Springs or if you have deep pockets Tein Flex coilovers and certainly a wider set of aftermarket wheels. Hope this helps some of the new guys out. later