In the current format, heroes are lined up automatically by level and fight accordingly until one team has everyone killed. Not much active participation, other than what it takes to click a button to join the fight. And also, as has been happening a lot to my team lately, when one team has a big player with tons of levels on the other guys, he pretty much cleans out everyone on the other team.
What about an alternative format where players have full control of whom to attack? This could be a 24-hour event, during which each hero can attack any of other team's members a limited number of times. A win scores one point, a loss and the point goes the other way.
We could incorporate this format into a tournament spanning several days, with teams separated into divisions according to their team honor, or average of individual honor. There will be a few rounds and at the end of the tournament, each division would have a winning team. Give them some epic gear for prizes.
This format would promote more strategy and more communication among team members. It takes skills and experience to know whom you have a good chance of beating. And because it is pretty much a team effort each time, players would get more satisfaction out of this and be more motivated to build their heroes and teams better -- and spend more real-world cash.