I do not thnk that the impact bumper cars will get very far along in $$$. Below is a link to one of the nicest ( in my lowly opinion) impact bumper cars I have seen for sale. Big motor, ac, SC/RS, nice interior good color. I don't know what the car sold for but ask was $120K
Let me just say that is my opinion, and there will always be cars that will bend the rules somewhere. Not saying they are not appealing or popular just not going to pull really big bucks.
I just bought a project from a friend that we had been helping along, originally a guards red M491 sunroof coupe with 88K miles. I had recommended backdating so when he tired of it he would at least get his money back out. He wanted to do his own thing, big brakes, big wheels and tires, roll bar, iroc bumpers, keep the stock motor and ac. Well 3 years later I picked it up and will be backdating it. I think this car would be hard pressed to get the result of the SC/RS finished in a short hood IROC style. But I am thinking it will do quite a bit better as a long hood, with smaller brakes, smaller wheels and tires, we'll see soon.
http://forums.pelicanparts.com/porsche-cars-sale/969135-1984-porsche-911-sc-rs-954-homage-w-3-6l-twin-plug-socal.html