I don't see the point in protecting admins from (spectating) either only because you're already able to hide your admin status. It's marginally beneficial for anti-trolling if you're dealing with a particularly paranoid troll but there's going to inevitably be randoms spectating occasionally and that isn't much of a deterrent itself. So if I was trying to clandestinely admin from spectate then all I'd have to do is operate without the indicator.
The hide feature works very well as far as I can tell.