Like all of Daniel's Fantasy issues, these were over struck on real coins; in this case real silver Washington Quarters.
A total of 831 pieces were minted, some with a Bicentennial reverse and some with the normal reverse seen here. For this particular die combination, 176 were produced. You can see the various possibilities at “1933” and “1975” Washington Quarters – Production Blog.
I don't see this particular piece attracting much interest over time. There's really nothing special about 1975 other than that no real quarters were made that have that date. Many collectors wouldn't even realize that it is not a genuine coin!
Clue for the second 2014 Silver Eagle Giveaway: The rain in Spain wouldn't have saved him.
Contests and giveaways: http://coins.aplawrence.com/2014/05/contests-and-giveaways.html