Remember that the torque or manifold pressure you see in the cockpit is only a measure of the drag of the rotor blades. Less smoothness will generall mean more drag, and when you run out of power to turn the blades at higher angles of pitch, you run out of lift.
So, keep smooth, clean blades, and if you fly in heavy rain, take the time to get leading edge blade tape, and keep it in good condition.
I'm surprised no-one makes a kit of some cleaning and waxing solutions to keep blades clean. I understand some manufacturers specifically prohibit waxing the blades - can anyone elaborate?