Amir, interesting collection. The Bell wing nuts came on some pretty high end French bikes and they are scarce and hard to find thus the reason for the high prices in some markets. You will find that not only Japan will pay crazy prices for the Bell wing nuts but you will get a good price in the US for them also. Of course there are size differences (something I learned from fellow CR members) and those have different values also.
Also, you might find that the term wing nut is used for more than just the mechanically threaded fastener. It can be a term of endearment or not. I have been called a wing nut in my time and I know a few other wing nuts in hte hobby.
Cheers
Ray Homiski
Elizabeth, NJ