Not a bad idea, though I'd probably make the vendor offer more things at once, instead of forcing the player constantly refresh his wares, when searching that one specific thing.
When we're at it, I'd probably even add some sort of library to cities, like in D:OS1, but with a vendor inside who would sell random books, including crafting manuals (or maybe those could be sold by the crafting material vendor), and he'd refresh his stuff just like a normal vendor.
Anyway, I thought you could use higher level essences to craft stuff that required lower level ones.
