Yeh, I was perhaps understating it when I said it was “quite over-complicated” 
I’ll be putting up an optimised version with a simpler material function call sometime soon.
Regarding the FPS, I only lose ~1 FPS when the dust layer is enabled across the whole scene (I set up a simple keypress function that toggles the MPC DustAmount from -0.1 to 1 in-game). I have fairly old PC running a 770 though, so anything above that will probably not even notice the hit.