Yes, increasing the house edge slightly would probably give investors more profit, so long as it stays competitive with other gambling sites (I doubt people will change their minds about gambling at just-dice due to a 1.2% house edge vs 1% for example).
I don't know how true that is. PrimeDice and CoinRoll offer pretty similar services to the player, and both offer a 1% house edge. I personally wouldn't play at a 1.2% game when there's a 1.0% game next door. My feeling is that the loss of bet volume caused by increasing the house edge would swamp any investor gain from the slight increase in house edge. I can experiment with this later, but I think it's still too early to be making such changes.