Hey rgbox,
What you want is a solid wireframe and this is currently not possible in Away3D 4.x. This is being considered as a feature request. Reasons for this discussed here: http://away3d.com/forum/viewthread/779/
Not offering a wireframe material (or a solid wireframe material per se), we do offer wireframe primitives, which are just primitives constructed from line segment entities. They have nothing to do with the regular primitives and cannot have materials applied to them.
Regarding your second question, I’m confused, you say you used a wireframe material when we don’t have one as I just explained. What is it exactly that you’re doing?