I've been observing the use of these codes I posted (gave out ~1.5 BTC on the site so far). Pretty much every single time all the coins are spent on the next upcoming game, and the users never even log in, they just get the automatic withdrawal for whatever they win. Some people just claim the promo coins and don't even use them.
Not sure if I mentioned this or just alluded to it when I was giving my feedback last month, but giving away the house to random people is a bad idea (as you found out). People just want free shit, they don't want to play a game. If you have a budget for promos, the better use of it is to use it to fund promos that encourage participation. For example, fund a "most wagered" leader-board for a week.
The idea is still great, but as it is now it holds no interest to me. The bets are so tiny and because of the parimutuel aspect of the site and the low userbase, any bet is basically going to be laying 1:3 or so which is horrible odds. If there were more people playing, leading to bigger pools it would be great. Good luck.