I'm sure this has been thrown around your team for a while--and I'm not the first to bring it up...but how about giving some old missions replayability with Valiance mode?
Increase in payout
Increase in elite mobs
Increase in mob HP
20ce per elevator
A timer at the beginning of each stage and a leaderboard for level completion time + score for 1-2-3-4 players (score being the payout and acting as the tiebreaker if completion times are similar)
Elevator passes make it too unfair.