In the opinion of the forum, what would be the best use of gems in my kingdom and what are the best uses in general?

I have already purchased 2 Wizard Schools using the 75 gems I got from several other game goals and I am currently sitting on about 30 or so. I don't spend money on the game. I probably would spend a few bucks here and there during a sale, but I refuse to unless the gem traps are cleared up.

I was thinking of buying a lemon tree. It's the only fruit tree I don't have, and I'm in the middle stages of the game with a severe iron shortage, so I can only hunt bandits when I get 5 swords from Thurston's Fort.

I was also thinking about the Royal Manor, although it's kind of useless until it gets upgraded a bit. I do, however, like the idea of using gems on things that cannot be obtained any other way. Also, I am sitting at about 2300 RP trying to devise a way to get high enough for Sabina and the Roost.

Any advice would be greatly appreciated!