I have a few old Casascius bitcoins. How do I keep them in good shape? Should I have them graded and slabbed?

Related info:Some are 2012 brass. I also have a couple silver ones from 2013.Yes, they are loaded.The brass ones are in OK condition. No great, but not terrible. They don't look shiny like when they were new.The silver ones look pretty shiny. They came in a clear plastic case.I keep them in a small felt-lined box, hidden away in a safe place.I noticed these seem to have gone up in value quite a bit since I bought them. The reason I ask is because the brass ones don't look as good to me as they used to. I don't want the silver ones to lose their shine.My questions:Am I doing something wrong in the storage on my coins?If I have them graded, will that help the value? (I don't want to if I don't need to. But if it's the only way to preserve them, I will.)Will the silver ones be OK in their little plastic case (the one that they came in), or should I worry about tarnish?Will the brass ones get worse?edit: Added a questionnote: Throwaway account, but of course I'll check back for answers. Thanks in advance for any replies. via /r/Bitcoin http://bit.ly/1oJ6K5M