This is a very good idea of balance of space(amount of coin). Another balance of time is to limit the showing time of coin. For example, if a coin has not been picked up in 30 minutes, then the coin will disappear and randomly display in other pools. This mechanism will largely activate the game. Now some people united to divide map into different parts, and sleep for 2 hours after 1 hour of game. When they wake up, the pool are full of coins, then they collect all(I guess that if someone acts as a hardcore player for long time, he will become machine,OMG). This maybe  the reason why the price of HUC is so slow and  many players leave it.