you are correct, but you left out the Islands that get shown to logged off users. eg: online_now.php and its siblings, which if enabled would show to logged off users along with logged in ones.
try logging off here as a test. you'll see the lotsa islands with info about users on the forums.
you are correct about the xxxx.inc.php scripts though, but that will be perm-matrixed for the most part in 7.3.
so, yes i see where you are driving at, but there are some other things that might need working out to completely lock left/right column info from logged out users.
shoutbox is a classic example where there is a one liner elsewhere (ubbthreads.inc.php -- 7.2.2) that needs changing to hide it from guests.
