I noticed a huge flux of wealth in this game. One idea I can think of would be to introduce a lottery system. Example: 100k coins to enter. Say 100 people buy in. That's 10mill gp. A winner is selected weekly/monthly. 60% winnings go to the winner and 40% goes to the "game". I see two positives for this. 1) someone just won 6mill gp for 100k investment. 2) 4mill gp got "wiped" from the game.
It will help keep things balanced. I don't know just food for thought.
Kryptix's cornflakes had the perfect lottery system built right into the game client. At any time he could start it and a box popped up. you typed ::lottery to enter as many times as you wanted for whatever the entry fee was for the given lottery. It went on until he decided to stop it and it randomly picked a winner. More you buy better your odds. (Or so the theory goes, haha!)
I never win at these damn things but it would be fun.