How I see getting gems from killing mobs is; Personally, I feel like it is already quite easy to boost your economy and get gems/crystals.
I expected killing mobs to give 0 and that would be extremely balanced.
Then I found out that mobs give gems when you kill them and I thought; Well that's a bit broken.
Then, I found out that they have a chance to give extra gems/crystals and I thought; Well that can be abused.
Then, I got 5 golden gems in a row. (Worth 5 gems) and I thought; That was easy.
Also, I've found there are to many seed plots. Something that I think there needs to be more of are challenge rooms.