I, for one, would like the developers to allow you to get back the same number of resources you used to 1) build & 2) upgrade your various mines. That would compensate for the actual remaining product you're losing IF you tear it down as it nears the end of it's usefulness. If you level up to 3 on your mines, I think you should get back the actual cost to get that mine UP TO level 3. Fair's fair, IMHO.