What if the Paint Tool to apply materials had an option to paint on a material in a specified thickness? Pick the Brick material, set the thickness to 4" in the options bar, and now it 'paints' on 4" of brick in the specified area, which would then be a part of the model and show up in sections, details, etc. If the thickness was 0, then the Paint tool would work as it does now, and just paint on a material. I think this would be a great way to do vertically compund walls.
Another example: floors, build the floor structure with the floor tool, then select a tile material, set the thickness to 1/2" and paint in the tile with thickness. Switch to Wood, set the thickness, now apply wood flooring.....you would still need to split the areas to receive the materials.
Another thought, it would be nice if it worked like SketchUp, in the sense that you could draw a line on a wall, and then 'paint' in a material with thickness, rather than having to use the Split tool.