When playing the daily challenges i.e. hunt for food, it would be cool if the heroes that are assigned to go into battle earn level points based on degree of difficulty. This way rather than just rolling through with your top team, it gives the play the incentive to play their lower teams and grow them.
Also, when you do train using other heroes, the type of hero you use to train your hero ought to mean something. If you train a green with a bunch of red heroes, they should be stronger against red then one that trains with a bunch of blue.