I think you should be able to sell items in the crown shop for crowns, I have some items that I bought from the crown shop ages ago, since then I've bought better ones, and the old ones just sit in my bank because I don't need or want them anymore. I could sell the old items in the shopping district, but I feel like that's a bit of a rip-off, considering I paid crowns for them and all I get back is gold. (I have WAY too much gold anyway!) You wouldn't buy something for dollars (a currency that you use) and sell it for yen (a currency that you don't want/need to use) because it's a (for want of a better word) "stupid" idea!
Sorry I went on a bit, but I feel strongly about it
pyromancer.