When you go into Mission Mode, you are allowed to redo missions you once did, either with friends, or by yourself. You complete the missions and get a certain ammount of Crowns or whatever they are based on your performance.
Not only that, in the story mode, different characters in the Gray Area, depending on where you are in the story, give you better items than your could normally find/buy/redeem. They might have certain criteria such as having an item, opening chests, etc.
That's what I've figured out so far. As for my last post, I guess it's not true. Xion's hood problem didn't happen again from those two days on.