i increase my idle speeds with a program that came with my asus mobo, called fan Xpert2, you can set the fans to the desired speed. its not that risky, unless you have a bunch of fans and crank them up all the way, the psu might not be able to handle that. (depending on psu model of course)
or you can buy a fan controller that usually goes into a bay in the front, and it has little knobs that you turn in order to change speed (or they can be touchscreen)