On a reasonably fast machine, an idle Finder shouldn't be using more than 0.5% CPU on average. You'll see the occasional spike, but most of the time, it's not hitting the CPU at all, unless something's wrong.
Also, I have enabled "quit finder" with Tinker Tool, and it works here just fine. Quit it last night, and re-launched it this AM no problems. Was curious to see how much it would speed up RC5, and the answer was not much.