I have been drinking Kava regularly for two years and feel equally or more sensitive to it than initially. If it is true that I get used to the sensation of kava, I'd say that helps me know what to look for when imbibing. A 3 day break does seem to give magic to the kava experience, however it is really hard to tell, I believe there is no diminishing effect for me with kava.
Tolerance, yes, I'm pretty sure I can drink more kava than I used to. However one of my friends has been drinking kava with me once a week or every other week for a year and keeps up with me quite well with no complaints. Which leads me to believe my tolerance for kava is psychological. If I truly had a kava tolerance, I should be able to shell circles around him, in my theory.
I look forward to hearing responses from others who have more knowledge and experience regarding the subject.
In my personal experience I have not assessed a tolerance or withdrawal with kava in any regard. I drink 40g per night and have for over a decade. That amount still hits me more or less the same as it always has when taking into account the general fickleness of kava's effects.