After sprypainting the road black, I dedided to try some grey dry brushing. This caused some of the grit to come off, but otherwise ok. I'm not sure that the road requires dry brushing and that just leaving it black might do the job ok. I might do another strip without the dry brushing and take them both along to my next gaming night.
The mud road was looking ok, but it has a habit of warping overnight.... I might try ironing it and then dry brushing it if it dosen't warp again.