Anyways, it was actually pretty easy to setup. A custom renderable which overrides the targeting of all of its children. The children then render to a texture, which can then be reused. In theory and everything. A quick test works, but I've not the time to hack this caching into the mapdisplay to test practical benefits yet. Assuming of course I don't run into tons of problems I don't even know exist. Poor odds... Perhaps tonight, perhaps tomarrow.
Quick hack caching into the test layer and the coordinate layer. For some reason the rendered-to-texture is off by 1, and a quick search yields no results... Used a ShadowRect to make it off by -1 when displayed. Icky.
In better news, the simple changes bumped Release mode FPS from 18 to ~47-55. Caching the other layers and caching the different layers into one should help even more if needs be.
Still need to get off my ass and get things working; unit movement, player orders, turn transitions, the whole project structure, buildings, FoW discovery... Pretty much the entire game. I just need to focus on the basics, and build up/out from there.