Maybe use some of the money to upgrade a current app to the ad free version? I did that with a weather app and a solitaire app and have no regrets! A magazine subscription is a good idea too.
As for castle story...by fish shop do you mean the fish market? Or the bait shop w/the blue and yellow awning?
The bait shop is a total waste of gems. It only drops the lures you can craft in the magic forge.
The fish market does very rarely drop smoked fish sandwiches and other fish dishes. I often get coins only since I'm always maxed on catfish and butterfish. Occasionally I'll get 1-3 gold (regular) fish. (Not often enough IMO)
The Cabbage hut is quite nice to have because for now, you can store up cabbages until a prize you'd like shows up in the tent. There is no reported limit of rotten cabbages in storage. (But as we know, things are subject to change.) So far, I'm happy with that purchase, even though I THOUGHT I was spending coins when I bought it, it has more than paid for itself.
* although...depending on how long you're willing to wait for the cabbage hut, you can now get it with gold troll tokens, no gems required.