That's true of rare things in general. They get more expensive and desirable as they get rarer, then they cross a threshold where they become so rare that they

That's true of rare things in general. They get more expensive and desirable as they get rarer, then they cross a threshold where they become so rare that they become little known and demand goes away. (My dad had a car like this.) I think there is a reason why you regularly see stories about rare things being auctioned for record prices: it's an part of the publicity campaign to increase public awareness, thus maintaining demand for those rare things.