I have created a few really useful mline styles ...
Since almost none of my work is done in 3D, I use an mline to represent a shelf and rod for closets, 2 different styles for kitchen cabinets and bath cabinets and a footing/stemwall mline style. These allow me to draw multiple lines simultaneously, automatically offsetting them the proper distance. I tried them for different size walls, but found that to be cumbersome, since most of the walls end up being cut/trimmed several times during the edit process.
They have greatly improved my speed in certain areas and I would recommend that before you discount the effectiveness of mlines, you should examine your drafting process a little deeper. It may turn out that they are not useful to you, but mine has proven to be very useful ... and I stand by that.