Captured weapons and booty is a by product of the conflict. Russia has been stripping bases, this serves in preventing future attacks. It would be stupid to destroy everything. Georgian troops have rapidly retreated or deserted, most likely lot of equipment has not been destroyed. Also they will analyse captured equipment to see if they have been modified by western technology. As like you said to want to test them out to see the advantages these systems have. My speculation would be more valid, if I knew exactly what technology was provided by the west. Russia says Israel sold 200 million dollars worth of military goods including drones. For example, if Russia can get hold of some intact drones they will have access to advanced optics, at moment I know they have shot down many.