Currently you are not able to do quests that are any higher than one above your actual level. I thnk it would be more beneficial to increase this restriction to 5 levels above your current level. This would help to eleviate the oh so troublesome running out of quests to do problem.
It would also add an additional level of difficulty to the game if players were trying to do quests that are 3, 4, or 5 levels above them.