Your list seems accurate at the extreme ends, but not in the middle, in my (limited ) experience. The ENTP and ENFPs I know are definitely more extroverted than the ISxPs. My ISFP bf and I are both pretty introverted, by pretty much whatever definition you want to use. Definitely more than my good friend who's an ENTP, or ENxP acquaintances. We might like to go out and party or whatever in short doses, but it's always a relief to come home again.
So with that in mind, I'm not sure that S vs N has more of an impact than I vs E, though I agree that Ss would tend to be more extroverted than Ns of the same type. The theories about the other traits seem reasonable as well.