I was thinking that demolishing buildings should give you back some materials and disbanding units should give back iron and materials, depending on their weapons and armor.  Building materials and unit equipment would not just disappear but would be reused.  Of course not all materials should be returned to your stockpile as some would not be recoverable and no gold should be returned because it was used to pay for the construction, workers, soldier's pay, etc.

Also demolishing buildings should not make them disappear immediately, it should take a turn or two to remove the building and refund some of the materials.