This is the state of my UVs after multiple attempts and different techniques:
I couldn't get the UVs working, since simplifying the mesh made a mess of the order. After many searches using terms that SHOULD have revealed the results, a totally weird and random search landed me on triplanar mapping which is a technique for applying textures without the use of UV coordinates.
The good news is it works, mostly.
There's still some blurring/stretching at corners, but it's usable enough that I can put it in this week's build and apply my mesh simplifier to SOME geometry (mostly cubes and terrain). The other tradeoff is triplanar mapping is expensive, it triples the render to project each side. That said, it doesn't really affect performance on my machine as much as the reduced tris, so it should be a net gain overall.
While this reduces tris, my mesh simplifier doesn't work for more complicated meshes like houses, which means the tris are still high in town and performance suffers as a result. Still, it should be better than it was.
* Improved performance