+1 on the merge debris fields. It could work where each debris entity simple consolidates all the overlapping risk/reward metrics, and even if you have partially mined out a field adding to it with newly destroyed fleets simply updates those metrics by adding them to the existing leftover metrics.
As far as the interface mechanics goes, we should get a slider that shows how much risk we are willing to take, with more risk pulling more "richness" out of the field, at the expense of risking more of your tools/crew. As the slider goes up your % recovery goes up, but so too does the crew and tools you have to commit to the action, all of which are at risk for loss. There should also be some kind of indicator for the size of the expected recovery, like maybe a "you expect to recover 100 units of materials (all kinds)" so you can know if a particular field is even worth your time. Even better, put the field "size" in units on the map view (larger fields with more recoverables return a larger radar signature).
