Is water pump replacement and fuel system cleaning usual scams?

If it makes you feel better, you can wait until the pump fails completely before you replace it, but the "cotton candy" description is accurate of what a small leak looks like on a Toyota with the red coolant. You have to remember that a very small leak will 1) only leak under pressure, such as when the car is hot and running, and 2) will evaporate before it hits the ground when the car is hot and running. I'm not saying that you're service advisor is right, as I have not seen your car, but the description of failure is plausible.