Specifically, I think characters should have a flag on them for if they have awarded you XP, much like how knock out works. Let players earn XP through social situations, and have them provide no XP for kills (like the prolouge mindflayer and commander) unless a special event resets their XP flag (ie a certain conflict in the grove). The most grotesque abuse of this comes in the form of pursuing dialogue options for special rewards/events (like in D:OS II), and then turning around and killing for XP ontop of whatever reward they earned.
You have created a story, and rewarding players for exploring it should just as bountiful if not more than murdering everything for XP.
