The problem with avoiding fights and giving XP for that is in my opinion that you can avoid the fight => gain XP, solve the quest => gain XP. Then come back and kill the lot anyway => gain XP. This needs to be balanced properly for all playing styles.
Good point! It would be so much easier tojust give XP for kills and quests. It just makes the whole concept of sneaking and taking back doors useless.
Can they rig the maps so that you can take advantage of environmental factors (walls, bottle necks, poison barrels, etc.), but only if you can sneak over to them? That would make sneaking useful, while providing XP for kills.