I would wager that most cars that are tracked are better maintained than those that aren't. It's simply unsafe to have a poorly maintained car out on the racetrack, and many if not all PCA regions require a "mini-PPI" every year before they let you come out to a DE. Performance issues are also likewise dealt with promptly, as they will cause slower laptimes.
Yes, they're probably run harder than the average garage queen, but with a proper PPI, there's really no reason to not buy one, IMO.