It's certainly not worth nothing!
Using 1 July 2003 as a starting point (that's the period before the NSW lease started, but it is the period when big contributions started being made) I agree that there's been about $5 billion in grants, equity and debt funding.
But you clearly have a better business now than you did then - first mostly-complete year of the NSW lease there was about $250 million annualised access revenue (excluding CRN). Last financial year that was about $720 million. Not far off three times higher. Depending on what floats your boat, reasonable measurements of underlying profit have risen by perhaps four times.
Undoubtedly some of the money spent will never earn a financial return - hence the ~$2 billion of impairments over that time. That was known ahead of time (though perhaps not the extent). Some of that non-commercial spend can also be considered as the payment for the Hunter Valley part of the network - remember they got that otherwise for nix.
The latest report values the infrastructure on a discounted cash flow basis ("what can we earn from this in future") at about $4.1 billion. If you consider the grants and equity together ($4 billion) plus whatever the company was originally worth (say $0.2 billion from 2003 report) - so $4.2 billion total - that's then bought you a $4.1 billion asset less $0.9 billion loans and bonds - so $3.2 billion total.
You are $1 billion in the red - over ten years that's $100 million a year, which is a factor of five less than $500 million a year.
In terms of regulating these things, I think there is a need for some caution that the cost of regulation doesn't get excessive. I shudder at the amount of time that must be put in by the ACCC, ARTC, operators and customers for each access undertaking review.
Speaking from experience of undertaking a few regulatory reviews, the costs of undertaking these reviews generally aren't that high - maybe an additional $0.5M per annum. A large majority of the work that is required as part of a price/access review is required as part of everyday business operation and interaction with customers. Examples of this include asset management planning and growth servicing plans to negotiating agreements to provide track access and standards of service to train operators or consultant reports on the weighted average cost of capital the businesss should have.