Yeah.... G3 collecting has very little nostalgia factor right now (though that may change!) and so they don't hold much value.. . yet. Collectors bought G3 MIB as it was released, and did as they wished (opened it, kept it MIB, bought a 2nd), but secondhand selling G3 is nothing like selling secondhand G1!
I really think we have to wait until the next dearth of ponies on store shelves for the value in MLP in general to rise. Not just G1 but all the other generations too. Someday people will be paying high prices for G3s but not while you can still find bins of them at yard sales and all over Craigslist and given away to little girls who "will play with them"... well, in the abundance you have described. There are millions more units of Sunny Daze and Rainbow Dash and Pinkie Pie than when Hasbro released Medley and Starshine and Moondancer! Until there are much less available in the supply, there will be little demand. I would store them if you have the space and pull them back out again in five years if the market has improved any.
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