my family has raced street stock/hobbie stock/bomber type cars for many years...both my mom's side and my dad's.You would vomit to see the cars they have destroyed.At first it was old coups,then on to 55-57 chevies...then on into the muscle car type stuff... One was a 67 SS Chevelle..had a hole cut right in the middle of the SS hood, more CHEVY II'S than I can count..several camaros and the last 5-10 years it has been Monte Carlos.Obviously none of these cars were rare at the time.
If everyone saved them all they wouldn't be special. Besides,most dirt track cars are built from worn out junk cars and are not nearly as good as they look from the stands.Often they take cars that are wrecked or really rusty...they just use the skin of the car for the most part and they cut out the wheel openings etc so that takes care of any rust in that area..