Drill down through your SketchUp model and remove materials en masse using the SketchPlus Unpaint tools. Paint faces across the boundaries of groups and components using the awesome Deep Paint Faces tool.
With Deep Paint, you can click any face in your model to apply a material without having to repeatedly double-click into the containing object. No matter which face you click, the material will get applied directly to the face and not the containing group or component.
SketchPlus comes with three Unpaint tools that work on either (1) ALL entities, (2) groups and components, or (3) faces and edges. These tools are incredibly useful for removing materials from SketchUp models imported from the 3D Warehouse or other external sources.