[MrEyes]

In the end I went with this:

foreach ($vbulletin->forumcache as &$forum)
{
	$forumperms =& $vbulletin->userinfo['forumpermissions'][$forum['forumid']];
	if (forum_accessible($forum, $forumperms))
	{
		$forumids[] = $forum['forumid'];
	}
}

function forum_accessible($forum, $forumperms)
{
	global $vbulletin;
	
	if (!($forumperms & $vbulletin->bf_ugp_forumpermissions['canview']))
		return false;

	if (!($forum['options'] & $vbulletin->bf_misc_forumoptions['active']))
		return false;

	if (!verify_forum_password($forum['forumid'], $forum['password'], false))
		return false;
	
	if (trim($forum['link']))
		return false;
	
	if ($forum['displayorder'] == 0)
		return false;

	return true;
}