Dribbles raises a point, in which case the issue could be that the mobs don't drop loot appropriate for their level, a grim for example can drop only 1 rare part and give 5k for a kill but thats pretty much worthwhile if its a solo kill not for a group... The effort it takes to kill these monsters compared to the reward is the real issue I'd say.
also it would be nice to have places people could hunt solo though.