Jmmoric - I understand exactly what you mean, there is a cost but the question is cost versus benefit. There comes a stage when the benefit outweighs the cost, and if a mathematical calculation does not do it for you go with your gut. I am not promoting jobs for air traffic controllers, I am responding to a perceived risk of collision at Ballina aerodrome. This is clearly recognised outside of PPrune because CASA OAR has reacted to airline concerns, as has Airservices who no doubt has had airlines ask just when they might put in a Tower.
On your other point, my explanation to pilot colleagues of Class D operations is that the Tower sequences aircraft for the available runways; this with sight and follows, creates separation in the circuit area and on the runway. It also contributes to worldwide comments about controllers "over-controlling" Class D or providing a Class C service. This is inevitable when the whole point of air traffic control is the prevention of collisions between aircraft, (See ICAO Annex 11 Para 2.2 (a)) not strict adherence to ICAO or national airspace definitions. It must, in visual conditions, sometimes be easier and safer to de-conflict two aircraft instead of just giving traffic and then having to react to unexpected pilot actions.