You know what a great idea was in STALKER? When you were rifling through a body, occasionally you would be alerted to a place on the map where the ex-human had made his stash - where he his some ammo, radiation medicine, and medkits or whatever. The stashes were a real incentive to go off the beaten path and explore some new and possibly more dangerous parts of the Zone.
What if all the significant battle loot in open-world games were dealt with that way? It's a further drive to keep playing, which is useful in any sort of video game. Shamus Young tells us stories about "just keep playing" motivators like crafting systems, leveling, and small quests, and I think this sort of mechanic for loot could function very well as another such motivator.