Why are Superbirds worth so much?

Car and Driver magazine did an article, I think it was December 1988, about a 69 Charger Daytona. According to the article, In it's not so glory years, a guy used it for hauling plywood, from the roof to the wing!

Still makes me cringe.

I've always liked the winged cars, and still dream of finding one tucked away in a garage somewhere.