Boilover prevention and boild uniformity was why I previously posted on liking the idea of a PID controlling the boil. I am assuming you would want to position the temperature probe directly above the element (I have no idea at what height) so you get a meaningful reading. I am sure that the regular steam bubbles would provide a higher reading than 100C. Thus you could tune your boil to whatever temp you deem to be sufiiciently vigerous and/or cost effective.
And Chap, even if you are a PID-tard, a basic PID would mean you only have to sort it out once (perhaps with a mate if you were being serious) and then operate the switch providing power. You could even hide the thing inside a control box and shut the door, never to be seen again.