Yes, every time I change flavors at the minimum I'll change the water (and hose) and clean the stem.
This is probably why I'll buy a 2nd nice KM or similar hookah eventually. Usually if I have guests they don't want to smoke the same thing for more than about 45 minutes. So it will be convenient to have more than one clean hookah.
I could understand not wanting to clean things if you were say, smoking blueberry then switched to raspberry. It would be a nice mix. But that usually isn't the case.
I'll also pristinely clean every part if I'm smoking something that I really want to enjoy. I know from experience that tobacco tastes better from a clean hookah.