The avg interest people can expect get depends on the bankrolls size in relation to the avg daily betvolume on the site, but if we for example look at a situation with a daily betvolume of 10 times the size of the bankroll with a 1% house edge and a profit disturbution of  80% to investors/20% to site owner then one can expect something like 33.9% yearly profit on the initial investment if one left the whole investment in the bankroll at the site for a full year and 29.2% if one withdraws profits regularly.
Maby it could be a good portfolio choise to have something like 10% of ones capital in a dice site if it would have bets in BTC and perhaps 1-2% if it runs on some other digital currency.