The Nylon 66 was a novelty in it's day and it was a first rifle for many young shooters. There were lot's produced (more than a million) so their value tends to be among people who have fond memories from their childhood. In many ways the Nylon 66 was one of the very first mass production polymer guns.

My recommendation would be to take it out and shoot it. It won't lower the value and maybe you will find that it is something you like too much to sell.