Why are Superbirds worth so much?

Good old supply and demand. There were about 1920 Superbirds and only 503 Daytonas produced. And some of those numbers were race cars which were destroyed. Some of the street cars were stripped of the nose piece and wing to sell as ordinary Chargers and Satellites. The site www.superbird.com has much more detail. But most of all they were cool cars with racing heritage.