How about a Shared Loot System for the Plasteel/Diamantine ?
Lets say there are 4 Diamantine Caches in a Level, if your Group manages to find all of them, every Player gets 40 Diamantine (just an example) 10 per Cache.
I think this would Improve Gameplay and prevent the Rush for every Chest and grabbing whatever you can.
Maybe Implement a similar System for ammo, make it on the Proximity, if you are in Range, the other Players get 50 to 75% of the Ammo as well.