[Agema]

Most nations access 2-3 magic types, so will rapidly find 2-3 types of gems. (Although by my experience getting N1 mages is pretty easy, from tribesmen provinces.) T'ien Ch'i have a lot of magic paths, so you should have an astronomical gem income. Hire a few of the best multipath ones early, and march them from province to province searching the easy sites.

Secondly, a wide range of magic skills gives enormous versatility. I've forgotten the number of times I've thought "I wish I could access spell X", but my nation simply doesn't have that path open to it.