That could work. But I was thinking something on the lines of the GLA from C&C: Generals. Any vehicle they destroy drops a pile of scrap. If infantry or certain vehicles grab it, they get resources, if an up-gradable vehicle grabs it it gets upgraded.
The Maurader tank is a good example. the one on the left is the standard, and continuing to the right, is 1 pile of scrap, and 2 piles of scrap.
Or simply healing. That could work too.