I think you can make money investing in cars, but you had better be an expert in the market. For a while there, muscle cars were appreciating like crazy, but the bloom has gone off that market. Right now, certain models of the European exotics like Ferraris' and Mercedes are going thru the roof. The "average " guy would have a hard time being in the right place at the right time.
Another factor is that the guys who have a little money to invest in cars are getting older in the tooth. Their vehicles are coming into the market at the same time the younger guys are strapped for cash. Who is gonna buy these ?