Would be cool to see some really hard challenges like, "Defeat all the enemies in a specific order, 3x the reward" or "Take no damage, 2x the reward". Each mission would give you a random two challenges, and if you're a higher level than the mission, only one. This idea is taken from Dofus which I think this game is at least partly based off anyway :3
@zuul88, you can pretty easily beat the game without spending a dime.. Use your WBs in tournaments if you really want more, but they honestly aren't necessary at all.