No proper cost benefit study was ever done on this requirement .
Neither was it needed because the answer is so flippin' obvious. I sat 20nm behind one of my colleagues today at 350 out in the boondocks for an hour, not a word from anybody. One of us saving fuel.
In the US with blanket radar coverage then a CBA would be necessary to justify the ground stations verses replacing radars. In Oz, the benefit of providing the coverage in the first place is so obvious you'd have to be stupid not to see it not to mention the safety increase.
This discussion is analogous to someone wanting to ride down a freeway in a horse and cart.