I accept that the cache will end up depleted and can quite understand how it happens. I find ususally the kids take the bests stuff and the things I have for replacement are not always as good. I could stop the kids doing that, but then I have worked hard enough to convince them to come along. I'm not going to start arguing with them about what they take (I do moderate a bit). My response is to make sure I have lots of decent swaps, but I can not always match the quality of what is in the cache. As a result the caches slowly get worse - thats life I'm afraid.
The caches I set have always good stuff and ended up with tat. At least the kids enjoyed finding them, so I am happy.
Mark