There is likely an paragraph in the policy that excludes coverage for injury/damage that occurs while drag racing, so it is not quite as cut and dried as presented. Certainly, if you are just there to watch, your insurance isn't voided just by driving onto the property. And depending on what the policy actually says, it may even arguably cover you if there is an accident unrelated to the racing itself, i.e., in the parking lot or something. Then, once you leave, your insurance should cover you again. The entire policy isn't voided just because you went to a drag strip once.