For N scale dirt areas/roads I've used the lightweight drywall patching compound that comes in the pre-mixed buckets. I stir in some of my scenery base color latex paint (a light tan), then trowel on with an artists pallet knife. As it dries, you can work in ruts, tire tracks, etc. After drying, you can also hit it with various grades of sandpaper.
I'll have to try the part about misting with a hairspray or glue & then sprinkling on various grades of dirt to add textures.
