If you finished first your first time out at a Pro Solo, you might get protested for something like the taillight cover, but probably not. Now if you went to the Solo II Nationals it is a different story. I know of one car in the past that in Street Prepared was protested over removing the windshield washer bottle. There was another one that was protested in Stock over a seat cushion that had been added. It happens and if it does, the protest committee usually goes by the letter of the law, they don't say that it is something that only weighs less than a pound.

Someone mentioned the cover over the spare tire in stock class. Let me explain what happened with that one time. The rules say that you have to remove all loose items from your car. It also says you can remove the spare tire and jack. In a MR2 of some vintage apparently if you remove the spare, there is no way to hold down the spare tire cover, which you can't specifically remove. But since it is therefore a loose item, someone removed it. It only weighed about a pound, but the initial ruling was that they were DQ'ed, but a clarification later came out saying that it could be removed if there were no provisions for securing it in place.

Most protests are not really about cheating so much as they are about defining grey areas in the rules (like this example). Plain and simple, most people don't cheat, but they interpret things differently. Very seldom will you find someone running say a ported cylinder head they know is illegal, but they will see some area of the rules that is not quite defined and try to do something there. The rules are not perfect and they never will be, but it is up to the competitors help define these things.