While I'm all for alternative leveling-up methods, I vote against this idea. I love the fact that as I run through map after map, there're no quests anywhere. I've done them all, and that's something I'm proud of having accomplished. You have to take into account that some people do quests because they like doing quests, not just as a method for leveling up. By changing the current system to promote your style of play, you're undoing (or overly complicating) someone else's style of play.

Instead of advocating the ruin of a quest-hunter's play-style, ask for something new and original to be implemented as a leveling alternative.