Please purge your models before uploading to 3D Warehouse!

That would be the optimal approach for every model that is going to be inserted as component, and should be feasible since 3D Warehouse has been able to process .skp files for some years (remember before, when preview images where done on the client side?).

But: Not every model author would be happy if 3D Warehouse automatically modifies their files (at least the online copy of their files). There may be reasons to keep layers that are empty or materials that are currently not used. But these reasons apply mostly to work-in-progress and collaboration. And probably one cannot just throw out all non-component models, or require that all other models fulfill rules specific for component usage.

SketchUp needs to distinguish more clearly between collaboration sharing (Trimble Connect) and component sharing (3D “Component” Warehouse). See also eneroth3’s comments in this thread. I think for a specifically created components section one could enable automatic purging. But who is going to work through all legacy models and add those that fullfill the component criteria?