Why not layers or wall styles? Right now my methodolgy for dealing with renovation is to have the existing, demo and proposed all on the same layer (different layers for different floors, slab layers and roof) and control what is shown using classes. I already have a class for demo-wall and exst-wall that controls the graphic display of the wall, without having to move the walls to a new layer or having to change it's wall style.
So, during design of an existing structure, I can easily move walls between exst-wall class (walls that will remain) and demo-wall class(walls that will be removed) and have the graphical display of the walls change. Its is helpful to see where the demo-walls are in plan view, for existing load paths, etc, but I usually don't want the walls to have height in a 3d view.
I would rather not have separate layers for for demo or more wall styles to manage.