My feeling is that not enforcing the rules pi$$es off and discourages potential, loyal participants.
Once you(I) see that it's a free-for-all...... I lose interest pretty fast.
If I'm building a car to compete in a series, spend my time and money to build it right according to the rules, and then show up and see there is no real enforcement, I'd give it a short time to be rectified. If they continue to let things go unchecked, I'd find another venue to race at.

The rules are the rules, and should be the same for everyone.