You can either sell them for a relatively small amount of money or you can scrap them. Or, if you really like your rusty car, you can spend a bit of money on 'doing it up'. By this I mean giving it a paint job and taking real good care of it and fixing everything that needs fixing. It also depends on what car it is. If it is vinatge, 'do it up'. If it isn't, sell or scrap.
harmful
Depends on the climate they kept in.
The salt and the water will erode the metal
they are made with a paint and certin metals
He was baby blue
Wreck
They get very rusty if you just leave it there without ever using it.
As far as I know, there were only 13 Rusty Wallace Signature Edition 97 Thunderbirds produced.
They may become unsafe to drive due to rust weakening parts of the car.
roadways are wet , salt is used on roads to melt ice and it corrodes steel .
One reason would be exhaust fumes may enter the cabin area.
The car is safe due to the strength of the body. If it is rusty the strength goes away quickly. Also all the brake and steering parts are mounted to pieces that rust also.