I rooted only for a few minor reasons: to get the android market and google calendar. Both require you put a file in a directory that's normally read-only and then you can unroot, which I did. I have only re-rooted after updates long enough to fix those two functions (actually android market never stopped working for me but the google calendar did). Both are really a matter of convenience.
Beyond that I don't plan on doing much tweaking, for a while at least. I'm at the point with it now that it does everything I want. But not everything has been discovered by the hackers yet.