I've now done many layers of texture on Fat Face. Mostly they're layers of dirt and stains.
Since Mudbox doesn't support layer blend modes or paint layer masks or selections yet it's been assembled in 2D, just using Mud to do the projection paint to make opaque layers of whatever dirt, stain or patterning I've wanted for each surface. Even though it can't do it all yet, the ability to paint seamless layers was very useful.
I haven't done all the details yet and nor have I made a specular map. Those are to follow.