Figuring out how to get by without beating everybody sensless is fun in it's own way, but every gamer always goes for the most profitable way. Do I sneak around the bandit camp without being notice and gain exp for that, or do I KILL EVERYBODY and also gain mother load of loot?
I think there are two ways to balance this out. By following the peaceful way, the player earns more exp, or (and I think this one is much more fun) neutral NPCs and companions comments on your actions, and often, praise the player for choosing it. SImply, the world repfects your actions.