To me the most relevant problem with explosives seems to be that NPCs mostly ignore them.
So the Goblins purchased very expensive explosives but they do not react to all the barrels missing prior to their assault on the Druids. Then they happily stand right next to their own explosive barrels and wait to be blasted into the sky.
Solutions:
Reduce the number of explosive barrels or increase their weight considerably.
Make NPCs position themselves away from suspicious barrels. This should be pretty easy to implement as a perception check when an item on the "explosive" list is within a given distance
