I usually see LSD and Sways as being popular mods for AutoX. I'd go check that out. I'm sure there's some AutoX guys that will pipe in and give better suggestions. :p
To the warranty concerns:
I keep seeing this stuff about using only NISMO parts (not that there's anything wrong with them), just read the fine print on the warranties:
http://www.nissanusa.com/owning/faqs/warranty.html
Quote »Can I modify my vehicle or add accessories not authorized by Nissan?
Your Nissan New Vehicle Limited Warranty does not cover repairs for damage or conditions which are determined to be due to the installation or use of non-Genuine Nissan Accessories available at the time you order or purchase your new Nissan, as well as after purchase from your Nissan dealer.[/quote]The only advantage to using NISMO parts is that if one of those parts causes damage (which would probably only happen due to a poor install or poor driving habits, like driving in two feet of water) then that part that was damaged is still considered under warranty.
Installing most aftermarket parts will not completely VOID the warranty on all other parts. If you slap on a turbo and blow your engine or wreck your transmission, then it's quite obvious what the dealer will tell you... however, you bolt on a new HKS HiPower exhaust and take your car in for transmission service... they can't just refuse the service the transmission under warranty because of the modded exhaust unless they PROVE that the damaged to the transmission was caused by your exhaust install. Dealerships will probably try to scare you into thinking you have voided your warranty while you have NOT. Check SEMA regulations on aftermarket parts as well if you want more proof about warranties.
The same rules apply for any of the extended warranties.
Modified by Low_Cost at 4:10 PM 3/27/2008