I'm not sure which Nissan dealership you're going to, but I've had several first hand experiences with Nissan warranty's on 35's and they have been exceptional. You have to remember that the Japanese by nature are a very proud lot, and with this car they have alot to be proud of. There is no chance that they will damage their honour by disrespecting the number one most important part of everything GTR. That of course is the customer, if you've had the privilege of meeting the man himself, you will understand exactly how important it is to Nissan.
The official word that we've been given at track days is "with VDC on or in R mode there is no question all is covered." WIth VDC off, however (remember i's prescribed use in the owners manual.) If you suffer a mechanical breakage at the same time as VDC is off and it is clear that the breakage is due to the missuse or abuse (remember VDC off is only for getting the car out of snow or mud etc) that particular part of the vehicle may not be covered on that occassion.
One obvious exception is when a car is used in commercial competition, this is not covered. (Unless we are in Japan and simply lease your 35 from Nismo - track prepped for every meet - fixed price)
With mods, be cautious as most modifications will change the balance of the car and will result in slower lap times. (Unless thats what you seek). Obviously Nissan don't offer warranty for parts not supplied by them, however most of the manufacturers offer warranty with what they sell so really, what have you got to lose.