I like the areas to remain clear to but what if when they are clear you get a sorce of migration of friendly beings..be it traders,animals and the such.
I suppose its to much to ask to have a situation where when you clear an area say 4 traders move in and you can trade with them.
Or a small family builds a house and after some time gives you a quest...E.g you clear out the area in Azeroth and clear the troll cave. Then a family moves in(builds a house) and then a new set of monsters terrorises them and you have to clear the cave again.
Hence you have a sort of ladder or where accomplishing one thing leads to another. Of course you are free not to help the family or clear ot the troll cave as you chose.
This wil get rid of make the game less barren when you clear the area.