Hi Michael,
From my perspective 1,000km north, by playing RMx2, the Heath, Vic & Metro, you're essentially seeing the best of each style/variety of sandbelt golf. The one sandbelt course that offers an altogether different style to those courses is Woodlands, with its tiny greens. I would recommend playing it before the other 2nd and 3rd tier sandbelt tracks (Comm, Yarra, Peninsula, Spring Valley), because it's going to give you something you haven't already seen a better version of elsewhere.
Which is not to say the other sandbelt courses aren't interesting, fun courses that you'd happily play, but I always think that on a trip away from the familiar styles of golf at home, the attraction that reigns supreme is variety.
For that reason, I think the Wednesday and Friday you have free, and perhaps the Sunday that's currently slated for Yarra or Comm, would be well-spent playing some or all of National (Moonah), St Andrews Beach, Barwon Heads and Thirteenth Beach (Beach) -- prioritised in that order IMO. They are all terrific courses that are going to give you something very different to what you're already playing on the trip. You could also consider Healesville in the Yarra Valley -- an awesome 5000-yard course on hilly land that Mike Clayton's firm designed and built.
In terms of the day between Barnbougle and NSWGC, if you flew from Tasmania to Newcastle rather than Sydney, I could meet you at Newcastle on the Wednesday, play up there and then drive you guys back to Sydney for our game at NSWGC the next day. If you got onto Ellerston, this would obviously change your plans, but I would still think there's logistical merit in flying to Newcastle and getting a hire car one-way to drop off in Sydney. You'll save at least two hours of highway time that way.
If you can get on to Ellerston, I'd recommend playing it. It's a pretty singular, unique piece of design borne of a loaded client with a pretty dramatic site who told one of the best golfers to ever have lived, "build me the hardest golf course you possibly can". The result isn't everyone's cup of tea, but it's absolutely worth seeing and a handful of holes will hang in your mind. In different ways, it is both very much like Sand Hills and also the furthest thing imaginable from Sand Hills!
Depending on what time you need to get away to get to Adelaide (Nigel may have told me this already, but if he did I forgot!), we can play 36 at NSW or get a twilight round in at Bonnie Doon if you wanted to do that. Whatever appeals to you.