The idea is rather simple have a chance tied into monster spawn's to instead spawn a goodie pile, notable location or quest.

The adventure tree could allow for higher level piles, locations and quest's to spawn as well as possibly having a rare research that increased the chance, the basic premise here is that people are going to keep losing, finding or wanting things and possibly ask you to deal with it. It would also give us a good reason to keep exploring and battling monster's to get to the newly spawned stuff while at the same time cutting down on the massive amount of spawned monsters slightly.