Just saw the one where they ruined an 87 Vette. Looked like it was in prime shape prior to the show. Why must shows always ruin not only nice cars, but ones in excellent shape? The exterior on this was spotless, engine looked clean. I didn't see the interior prior to the show, but it couldn't have been that bad. Granted its one of the cheapest/least desirable Vettes, but still!
The point of the myth was to see if someone had to sell an otherwise good car for next to nothing because some corpse rotted in it for a month. You can't exactly do that with a car that was worthless to begin with.
While Mythbusters was bad enough, movies are much worse. They always make up several copies of each car, often having most if not all of them get destroyed in the process of making the movie. That's the downside to seeing nice cars in movies.