Racing not only can void your warranty, but it also can pull your coverage on insurance. Private tracks, auto cross, drag racing, etc. It's all the same. Excessive wear and speeds step outside the "normal" range the cars were designed to be used at. Excessive wear will cause parts to break early and increase costs to the MFR. In addition, excessive speeds also reduce your chance to prevent an accident, which is why the insurance companies will drop coverage if you try to file a claim when it was caused by "racing".

Now this isn't all "legal" terms, its just the way it is. I've been racing cars since 95, road racing, drag, autox, street, whatever. Just the rules of the game. You wanna play you gotta pay. I've killed motors, transmissions,etc. Paid for the repairs myself. Never held the mfr responsable. I knew the risks involved. If you are that worried about it, just put some tape over your vin number and take your license plate off.

I'll let you know though, I work for the business center here in the SW, and we don't deploy anyone to go to such events to check vin numbers or anything. Not too much to worry about. Our tech advisors can tell if a car has been modified or abused.