If I were going to do something like this for my own campaign, I would take inspiration from the game that is currently eating up my friends' time: Modern Warfare 2. In there you have to level up to get access to new equipment, and you have to perform certain accomplishments to unlock modifications to that equipment.
Like, you might get a nifty new machine gun at level 4, but if you want a red dot sight, you've got to kill 10 people first. Then if you kill 50 more people with the red dot sight attached, you'll unlock the thermal sight. If you get 50 kills with bullet penetration (as in, your target's behind flimsy cover and you shoot through the cover to hit him), you unlock extended ammo clips, and so on.
I wouldn't do it quite the same way, but I'd go for the same general idea of "let the player know there are things he can get access to if he takes the right actions."
For instance, tell the players that in every "region" of the world, you're going to include at least one martial exploit, one arcane spell, one divine prayer, and so on. The PCs can learn their own powers as normal as they level up, up to level 10, but they can also get bonus powers if they track down teachers, study under them for at least (insert timeline here), and pay some amount of XP.
So when they get to the ogre village, they might be able to learn the new ranger "chuck and charge" at-will from the ogre warchief, or pick up a warlock daily from the ogre who formed a pact with a demon, or learn an invoker utility from the woman who's leading a slave revolt. Any player could learn any of these abilities, so the fighter might pick up a holy power, or the wizard might learn to throw his orb implement like a shotput.
It would require just a bit of work, but I think it would make the game fun, because the PCs would be on the lookout for new 'unlockables.'