Why do we hide Special:UnwatchedPages from regular users? Unwatched pages are something that people should know about so they can be sure to watch them. If no one is actively watching a page, it's more likely that vandalism will stick around. Yes, vandals and trolls could abuse the info, but they could abuse all sorts of other features too, and that's not a reason to deny them to legitimate users. If there is any such threat, then that will just encourage legitimate users to watch the pages, thereby removing them from the list.
So I suggest we set $wgGroupPermissions['*']['unwatchedpages'] = true; in DefaultSettings.php. Or maybe 'user' instead of '*', if people prefer. Does anyone object?