Hmm, strange ... My XP reward for completing a quest comes higher if I have some levels more!
But it is indeed a very good idea to talk to many NPC's and mindread them to see if it give you a (side) quest ...
But there are also some quests that give no XP, but only gear and like Stabbey says, that gear have a better value if you have a higher level... but this last case I don't examinated it still on my own.
