And what are the rules of salvage in space anyway? Finders keepers.
The spacebot would have to change altitude and direction a lot. Somehow I think fuel would become a big issue. If it collected it would also gain more mass and require more fuel to change direction and altitude. Collecting does not seem to be the answer because of mass. It would have to be a pretty inteligent bot if it were to release water vapor clouds as well. You might inadvertently take down something important that can not correct it's own altitude quick enough.
I think the whole idea is a nightmare in logistics and devise, it could take a really long time to devise a workable solution/