Hey Gaz,
I was wondering if you could do a recruitment system. It wouldn't have to be crazy but it would help I think. Here's my thought
Recruit a person
Person spends 0-10 bucks = 200g
After 10 or more bucks spent 200% xp for 30 days one time only.
Person spends 10-25 bucks = Free stash tab
Person spends 26-50 bucks = Free hero of choice
Person spends 51-75 bucks = Free costume of choice
Person spends 76-100 bucks = Free ultimate upgrade pack.
Person spends 101 or more = special costume that can only be obtained this way(have multiple to choose from so it can be done by recruitment of multiple friends).
I feel this would encourage people to play with friends and get them to stay and spend money.