This is a great game and I wished you guys got really rich over it, and keep working on this game to make it better. Here is an idea for you:
Why don't you sell something that lets players erase the effects of the last game on their ranking? Maybe some special item like a magic pirate gold coins that you sell 10 coins for 99cents. If you screw up in a game and get a devastating loss, you can use a coin to cancel the loss of points.
I for one would buy some coins. It might skew the ranking, and yes, the ultra rich might be able to buy their way to the top, but if it makes you money, I can live with that.