It would be interesting to know if people providing services such as these are trained about what they are NOT allowed to do, otherwise they could easily, and to them, quite logically, ramp up their service level without realising the legal position they are in. I'll bet the Tyabb radio operator thought that he was doing a great job! (Incidentally under a duty of care scenario it would be interesting to speculate on where you would stand if you can do something, i.e see traffic, but don't pass it on because some silly book says so!)
I agree with the leave them in a room with no windows, or at least just the office window, otherwise they are bound to think they were given such a magnificent view of the airfield and circuit area for a reason! It is common sense to let the refueller or airline agent talk to pilots on the radio about weather and anything else he sees going on, but as soon as you train them and give them what to all intents and purposes is control tower, then that is what they will become. It's human nature to want to do your best.