I've noticed only once in my games did Resource Harvesting actually produce chests near my capital near my Metal/Clay or whatever i had.  Most other games it was simply a completely useless trait - in the sorcerer's case one you have to take to get through that skill line.

The one game I cdid have it working, it was insane.  Every turn I had one unit walk around and pick up the tresure chests and got a ridiculous amount of common crafting items.  

It would be better if this skill simply gave you an amount of items in your inventory commensurate with, say, the # and Type of each resource you control.  Putting in constantly spawning treasure chests is pretty annoying.