If the brake has no bite, changing the rotor will make f**k all difference. Just clean it, and then replace or clean the pads. Then don't forget to bed the pads in afterwards, this can take time and the brake will be poor until its properly bed in.
That is of course assuming that the brake is bled properly, set up perfectly, and there are no leaks anywhere which could cause the contamination. Some people will probably say one rotor works better than another, but there really isn't anything wrong with a standard Hope one.
Also, the Hope floating rotors aren't that great for trials. They can creak and develop play over time, a waste of money really!