I haven't had a chance to play LittleBigPlanet yet, but it's definitely got some competition in terms of player created content, I imagine. That's alot of levels and Boom Blox Bash Party already comes with alot.
Having completed a full level 40 character in Champions, I offer up that leveling is the main forcus of the game. I'm sure as the game develops and more mission content is added (like the new Nemesis encounter) then there will be more reason to go back and visit maxed toons, but for now Frank is really shelved except for the off chance that when I play him, I will get a Nemesis clue (which so far have all been new missions).
That said, there seem to be alot of players in the game who don't have a max level toon at all, and instead play around with their variety of different sets. I saw one person say that in order to enjoy the game fully, you have to make a character that fits your style, and that's definitely truth. Not all powersets are equal in terms of enjoyment, and there are definitely styles of play within them. I'm hoping that in the future they will also add more powers, since there are some that need more development within themselves, but the general core is there. I don't know, nor have I seen one person who is only one powerset (in the later stages. You're kinda forced to in the beginning.)
Even as I write this, I'm thinking of Retconning my second toon Talia, from electricity to something with a little more ranged punch.