Rarity is almost always worth more money and is in its own category. If I ever produced a two headed snake I would be on the phone to BHB in about two seconds because I have no doubt Brian would want it. A two headed snake holds no value for me but it is rare and odd. That in itself is enough to make someone pay big money for it.
As to your famous dinker.... On that day you were the smartest and luckiest guy in the room.