How about the next reward item being a potion or simple quest starter that results in a huge XP and AA boost. Some limitation would have to be placed obviously, such as no trade and only usable below a certain level, to prevent exploitation at the next level cap raise. I suggest enough Xp to take a level 20 up to maybe 65-68. This would still allow plenty of opportunity to learn the class before end game content without the drugury (to me) of repeating zones and quests.