Liability: I would never self insure, even if I had $$$ stacked to the ceiling. Well, to be fair, here in Canada we MUST have liability insurance on our planes anyways. Goes for every non-Canadian airplane entering the Canadian airspace as well so if going north is something you ever want to do, self insuring for liability isn't even an option. But, even if it was an option, I wouldn't do it. I don't see the point. I'm covered for $2M and pay peanuts for coverage, despite being a low time, VFR only PPL holder.
Hull: Sometimes I do, sometimes I don't. Right now, I have my Cherokee insured. The insurance quote was cheap (less than what I pay for my car somehow), I travel a lot this year, parking outside on trips as I can't take my hangar with me lol... I sleep better knowing that IF the plane gets caught in a t-storm or some idiot hit and runs it out on the ramp, I don't have to worry about it. It's less so about the $$$, I could cover what I have in it, but more so for having someone help and deal with it, if something were to happen. At the same time, in the past I have occasionally "self-insured" the hull value of a plane, especially when I bought a fixer upper I got cheap and the plane wasn't away from base very often throughout the year.