Here is an annotated map of the area from Google. If you compare with the map they supplied, you can see that they have labelled Old Gibber Road as the Mining Road.
Now the Mining Road was a public road for many years, linking Tea Gardens and Seal Rocks. It had been gravelled and was a very solid road suitable for mining trucks. The Old Gibber Road is just a fire trail, mostly sand, which is only used for firefighting and occasional access to Johnson's Hill. It is quite boggy in places, especially the side-road to Johnson's Hill. It was never open to the public in the history of the park afaik, whereas the Mining Road was.
We might presume that the purpose of this proposal is to raise money for NPWS. If they allow vehicles to regularly use the Old Gibber Road, it will deteriorate quickly. To maintain it as a viable access road for commercial activities will likely require major (and expensive) works to improve its quality. It is likely that the cost of this would far exceed the income derived from the commercial activities.
The most telling part of the background info they supply is this statement:
"For visitors, the Mining Road fire trail is in an area of the park zoned for its secluded setting and minimal infrastructure. The trail offers a more remote and self-reliant experience, compared to other more developed areas of the park."
So remoteness and self-reliance are the important characteristics. 4WD camping does not quite gel with this concept.
It goes on to say:
"Since 2002 the area has become increasingly popular for activities by individuals, school and other groups, commercial tourism and adventure based events."
I think they are stretching the point here. I imagine the rest of the park has been used for these activities, but I doubt if this particular area has been.