So, after tearing out all of the fasteners and repaairing the walls, I went down to Lowe's and purchased an angle iron system made by Rubbermaid. The system uses a horizontal hanger and vertical pieces to which shelf supports may be fashioned. This stuff looks pretty strong. Anyway, everything is secured to studs via three-inch decking screws. Our existing shelving clips right onto the shelf supports. It certainly looks like it should hold. I'm finished with plastic clips and anything that is secured to drywall alone.