Having something similar to Snowy's setup (R32 though) I'll throw my ideas in as well. I have a full weight street set-up and a very nice 3/4 cage - so I'm well over stock weight.
For me, some of the biggest advantages of a race car are (in no particular order)
- you can ditch everything behind the dash and just keep the dash itself, including the heater, water lines, extra wiring loom, sound deadening - some weight there.
- be far more thorough with your cage design
- do a proper job of ducting and cooling without the restrictions of factory equipment and placement
- more agressive weight reduction (remove side intrusion bars, fit lexan windows etc)
- change suspension pick ups to allow for a more track bias and greater adjustment
I've run my street weight setup for 5 years and it's been a great, reliable car. Yep they are more expensive to setup than a 2wd but if money is a critical factor then you can go faster for less in a different car. Comes down to what you are passionate about and what you can afford to be passionate about.
I think the only thing I would do differently is not buy a mint example and mod it for the track. I would buy the straightest, cleanest bodied R32 GT-R I could find with a blown engine and start from there - reckon I would have saved $10k - $15k right there.
Regards
Andrew