I don't presume to know what the majority of Nader voters think. But I have spoken to many of them over the years and I've heard reasonable positions on why they support him. The only reasons I've heard that correlate with your suppositions (which may be right for all I know) are that I've heard people say they believe he is for the little guy and that he is outside the establishment.
The reasonings I've heard is they believe he is intelligent, principled, his own thinker, a warrior and not one of the other parties' candidates with which they have become disillusioned. Accurate or not, they are fair reasonings. I know several of the same who won't vote for him again because they feel voting for them helped put Bush into the White House but still like him.
I'm not that disrespectful of a Nader voter. He has made contributions which I think were important.