Thinking about this thread at the Forge, which mentioned RPG "reward systems".
I think a reward system could be a "hamster wheel" if the way to earn gimmes and Currency doesn't actually encourage people to engage in the point of the game, nor encourage them to "drive towards" it. Basically, your Exploration of the game system should promote the Exploration of "what play is all about" (be that competing for glory in Agon, or wading through moral quandaries in Dogs, or making tough choices in ApocaWorld) by-way-of Exploring character, setting, and situation.
For instance, some games have it so that the rules for advancement (a common avenue for Exploring the game system) are detached from the "presumed" content of the game - - maybe you MUST seek out a trainer in order to improve your abilities, but the majority of the game is dungeon-crawling, far from the academies and gymnasia (where the trainers are), then people have to go outside the normal fictional "play space" in order to "earn" the encouragement to buy into the activities of the game.
"Gold=xp" editions of D&D have a pretty clear, intentional reward cycle, especially if you can't level up until you leave the dungeon: you need to explore "efficiently" and try to use all your cleverness and care to maximize your gold-haul and minimize your exposure to danger. Dungeon crawling, using gold=xp/exit-to-levelup, is different than dungeon crawling that's defined as kill=xp/levelup-down-here. Not better or worse, but one is more of a puzzle game with a combat element and the other is more like a combat game with a puzzle element.
Specific reward systems do more than just encourage Creative Agenda; they also encourage a particular taste or style of play. Each reward system has its own particular take on elements like competition, exploration, and theme, serving as different varieties of play of a particular sort.
In D&D0e, the emphasis is on coordination, detail-inspection, and careful rationing of resources. We could say 0e rewards Attention to Detail.
In Agon, the emphasis is on inter-player competition, individual acts of heroism, and exciting, bombastic command of resources. We could say Agon rewards Chutzpah.
These are related types of gaming, but they are nonetheless distinctive enough (due to their respective systems and the style thereof) as to make playing them each a very different experience.
Polaris vs. Dogs in the Vineyard is good, too - - in both games, your character is powerful and in a position of authority. But the crushing weight of world's end (in Polaris) means that, logically, to advance your character is to hasten the apocalypse - - you have to lose Zeal and gain Weariness to get better on your dice rolls. Each advancement pushes you closer to the end of the game. You can avoid this by being "weaker-willed" against the Demons - - be more agreeable with your Mistaken, more willing to compromise and let things go, and you will last longer. But you will also be giving the Demons more of a foothold in your world. Fighting your battles is the only way to prove your worth, but fighting ALL battles only hastens your inevitable doom. Sort of a gloomy, Ragnarok take themes of fate and destiny.
Meanwhile, in Dogs, your character is always right. People may disagree and try to block the execution of your judgment, but you know they're just demons or idolators. The big question that helps to twist this theme is: how far will you/must you go to get your way? You have to be very tactical when crushing heresy, all the while wondering if you really deserve the authority given to you - - sometimes your judgments ruin lives unfairly. It's much like running an actual religious institution: handling dissent and disagreement proportionately, deciding how many administrative resources to dedicate to handling a problem, and of course wondering all the while whether any of it is worth it, ultimately.