I was just messing around with some fun stuff like texturing a terrain with rocks, duplicating it, weathering the duplicate and setting it to foliage. Sort of worked! (The edges were too distinct). My feeling on paths is that it really has to be smudged out and flattened and otherwise built specifically in the terrain. Then you could make a copy of the map, select the road, and use that as an alpha channel for the terrain's texture.