If a car sits rotors will rust. I usually ignore surface rust on my rotors because as soon as you use the breaks a few times the pads clean it off. As long as it is just surface rust it is not an issue. Rust becomes an issue if it starts pitting. I certainly would not use a electric drill with sand paper on it because there is no way you will sand evenly. You will probably heat the rotor doing this and warp it. This sounds like a bad idea to me but I do not know what you mean by the kent method. So, take my advice with a grain of salt.