Longreach is the way I have planned to go, going to try and fit in as much as we can in the short time we have as i need to be there ready to go 3rd December and deployment date isn't far of, so I would like to do as much with the wife and kids before it turns to shit again. They love the theme parks so that is a definite stop.
Okay so you are talking 8 days in total. Some LONG drives required.
I'd say 6-8 hrs in a car max a day. Without STOPS.
So you'll need to be quite selective on what / where you visit as you really only have 2-3 days.
Example:
Day 1 - Syd to Grafton (7 hrs drive). Fill up with fuel at Grafton. Places to stay on highway.
Day 2 - Grafton to Springbrook / Advancetown (3hrs 30 minutes via Highway then inland and over border at Murwillumbah). That will give you time to check out Natural Bridge on the way (takes about an hour), Hinze Dam, and possibly Purling Brook Falls (it's worth seeing). You could possibly cram in The Best of All Lookout and Canyon Lookout as well (as they are a short walk from car parks). Canyon is right on the carpark. Stay overnight either in Advancetown (Cedar Lakes Resort worth a look).
Fill up at Murwillumbah as nearest fuel is otherwise at Nerang.
Day 3 - Check out Sea World, and either Movie World or Dreamworld (I prefer Movie World). Staying overnight at Advancetown is only 20-30 minutes drive away from theme parks.
Day 4 - Advancetown QLD to Roma QLD (6 hours 14 mins drive). Overnight in Roma.
Day 5 - Roma QLD to Longreach QLD (7 hours 39 mins drive). Overnight in Longreach.
Day 6 - Longreach QLD to Mount Isa QLD (7 hours 3 mins drive). Overnight in Mount Isa.
Day 7 - Mount Isa QLD to Tennant Creek NT (7 hours 51 mins drive). Overnight at Tennant Creek.
Day 8 - Tennant Creek NT to Tindall NT (7 hours 40 mins drive).
You could always vary the above with 9 hrs 45 drive to Advancetown from Sydney. Day 2 entire day at Springbrook/Nat Bridge/Hinze/Purling Brook. Day 3 entire day at Sea World / Movie World (I'd go Movie World over the other 2).
Whatever theme park you do check their site for what rides are open/under maintenance for that period.
That will give you an idea anyway, but Nat Bridge/Purling/Hinze are definitely worth a look when up in that area. Advancetown is in Gold Coast hinterland and should be cheaper than staying on Gold Coast / Surfers.