For anyone interested, we added a promotion that pays 25$ in Bitcoin per day (exclusively for Bitcointalk.org members) if you maintain the top 1 position on all-time leaderboard.
From what I've seen (in the past) on online casino's: the user with highest total profit barely changes. Once someone hits it, he can keep that position for a very long time.
Once someone has a negative profit, he has more to make up for and will likely be out of this race. A daily or weekly race for a Leaderboard might attract more users, as they're more likely to win this.