I know that bit of road and like you say great for plug chops and getting things sorted.
Like a lot of people here I've been riding dirt bikes at Menai since the 70's and have been very lucky to have dodged any fines but still take the occassional risk.
In the last year or so I've been getting out there on a mountain bike, which I can ride to from home, still enjoying the bush and all the familiar tracks but at a much slower pace and without the fear of a copper waiting around the next bend to spoil my day. Not any more. Came across the new signs as I was ambling along a couple of weeks ago and haven't been back there since. Fortunately plenty of other places to go mountain biking in the area.
Its ANSTO's land, at first I thought It was for security reasons, but bush walking is still OK.