I have a bunch, too, and was able to sell a few at the garage sale I just had. Of course the baggie with all the glittery ones! The little girl was just too cute, pulled in by the shiny ponies!
The ones I have left, not sure. I can try a lot on eBay, but I know they won't go for much. I have a bunch of the first two series, but no one that seemed rare or sought after.
I like the idea of charms, since they are cute. The Ponyvilles are my favorites, I have to admit...miniature things are just adorable!