I think that heavy weight stands are necessary not only to support speakers but to be acoustically inert as well. The whole idea of stand is first , to get speakers placed at appropriate level and second, not to add colouration to sound by intrinsic vibrations. A light weight stand is more prone to vibrations. Experts, please corrct me if I am wrong. Adding sand to centarl rod is a good idea but then the rod has to be strong enough to withstand weight of the sand in addition to speakers. Some bookshelves are pretty heavy, more than 10kg!