I would find it "logistically" more "realistic" and tactically more "interesting" if destroyed buildings, no matter if self-destructed the enemy's, would turn into "mines" containing the resources which have to be explicitly gathered and brought to one's storehouses.
Also a battlefield could turn into "mines" with the "loot", like scouring the field after the battle looking for usable stuff, although it's hard to determine when a battle "ends".
Would change balancing heavily against rushers/attackers in far away foreign territory though.
Instead of "mines", the resources could also turn into those bonus-/treasure-item-like things, although those don't have to be brought to one's storehouses.
