[Wavytone]

John, I did a fair bit of reconnaisance some years ago...

The closest site (and it's surprisingly good) is a big sandstone rockshelf on the escarpment off the Kings Tableland road (at the end of Hordern St), south of Wentworth Falls. It looks across to Sublime Point, and has good horizons in all directions.

Next is the Katoomba airstrip as Mental suggested, another 20 minutes up the road.

Then:

Hargraves Lookout, on the end of the Shipley Plateau Rd out of Blackheath. This site can turn on the most excellent seeing, but it is very exposed - best if the weather is dead calm. Hargraves has an advantage that being light sand/sandstone country, dew was never a problem. This was one of my favorite spots for many years.

You can also go down into Centennial Glen, but get in touch with the landowners so they know what you're doing first. It's a nice sheltered place to be if it is windy up the top. Another spot a few minutes away is the paraglider launch at Mt Blackheath, provided you don't make holes in the astroturf (which stands out as fluoro green on GoogleMaps).

Mt Banks and/or Pierces Pass (off Bell's Line of Rd), there are a couple of carparks; another favourite spot in years past. As with Hargraves it's light sand/sandstone country, so dew was never a problem.

The Lithgow Scenic Airways airstrip, it's a gravel strip further along Bells Line of Rd on the left a few km before the descent into Lithgow and easily seen on Google Maps. The way the road cambers (it's on the left of a fast sweeping right-hand curve with concrete blocks in the centre of the road) most people have no idea it's there and most miss it first try. Drive down the far end to get away from the road and its pretty quiet apart from possums squabbling in the trees.

Cathedral camping ground at Mt Wilson, sheltered if its windy, but roaming dogs can be a problem at night. There is also a lookout at Mt Wilson with room to set up a scope with a car close by, if interested I can find it on a map.

Hassan's Walls - Drive to Lithgow via Bell's line of Rd. While driving through the old part of town before you reach the intersection with the Great Western Highway, there is a turnoff to the left marked "Hassan's Walls". This leads to the escarpment which towers over Hartley Vale. Several spots for a scope, with excellent seeing, but dew is heavy there and those with SCT's will have trouble keeping the corrector clear.

The road to Jenolan from Hartley - there's a picnic area on the left before the descent into the Jenolan valley, I have observed from there once... bloody cold even in January. For that matter you could set up in the carpark outside the old Hartley courthouse and save yourself 90 minutes drive.

You can go all the way to Mt Canobolas but that's a very cold place to observe from and not really worth it seeing wise.

Further afield...

Mt Borah, 90 minutes drive past Tamworth; though you will have to make an arrangement with the landowner who might also let you stay in a cabin at his place;

Harrietville/Bright/Wandiligong in the Victorian high country, found a couple of good spots to observe from, good seeing and very dark.

Mt Kaputar, the best site I've observed from, but that's an 8 hour drive and a whole story in itself. Well worth going if you can make a group.