So I play Dungeons and Dragons Online, and one of the progression mechanics that they have is called "True Reincarnation". Basically, you hit level 20 (or 30 for Epic True Reincarnation) and you can go back to level 1 with a class-specific bonus.
That's obviously based off of MMO mechanics, but can anyone think of a tabletop game with rules that handle similar things? Basically, the way it works is by giving players an incentive to give up a high-power character in exchange for a low power character with a little boost over the average, allowing them to make new decisions and explorations while reaping the benefits of whatever they already did (like a bonus to sneak attacks, for instance, from Rogue).