Maybe it's just me, but I tend to use up about 2-3 lids and caps per 2oz bottle of CA be it thick or thin. I usually have 2-3 extra ones laying around that are caked with dried glue and no longer useable.

I learned at a fly in (from Gordo-Outlaw) that soaking the caps/lids in a jar of acetone removes all the glue. Just plain ole Acetone... it eats the glue but not the plastic. I came home, soaked a few for a couple of days and other than the exacto scratches from trying to clean them off previously, they look brand new! I know they aren't that expensive, but it's nice to be able to recycle them instead of tossing them after every build. Try it, it really works!