So pie in the sky, but here's what I would do. Keep in mind this is at LEAST a 5+ year plan.
Shut the place down for 6 months (Winter months) and do a complete clean up. Paint attractions, tidy up/install more gardens, full safety audits, remove covers from RHLR etc.
Throughout this process making sure that staff are well trained, the park is well kept and the park is well maintained.
Moving forward here are the projects I would look at putting in place:
1. Bring back the paddle steamer, including cleaning up the river.
2. Review and extend the railway including more stops (i.e. potentially bringing the line down past Buzzsaw, perhaps in the old Wipeout space, WWW entrance, Tiger Island, Wiggles World etc.) and bringing back the steam engines.
3. Upgrade ToT, they should have done it when they had the chance.
4. Complete retheme of Gold Rush, Buzzsaw has a decent back story so somehow incorporate that into the new theme. New area including 2 new flat rides, perhaps a suspended Top Spin to replace Wipeout, but with heavy themeing and perhaps something a bit more family friendly like a good haunted house style attraction similar to Disney. The as the centrepiece of the new area a woodie that can run along the back of RHLR.
5. Remove MDMC and build either a Hyper that utilises the island in the middle of the river (Think EuroDisney BTRR by going under the water). Alternatively using the same space a B&M Dive Coaster.
6. Remove HWSW and replace with something new from RMC or even S&S (Steel Curtain at Kenneywood looks like it is going to be awesome!)
7. Next up is the old Thunderbolt site. New world for Dreamworld. Centrepiece is perhaps an RMC Raptor. It's close to WWW so lets try and fit some sort of boat splashdown dark ride in the area (Think Jurassic Park at Universal), who doesn't love getting wet on a hot day! Only because it was also mentioned recently on Parkz why not also look at a Freefall Drop Tower. So looking at themeing for the area i'm going with the Lost Mine (Freefall could be themed as an oil tower, boatsplash as the mine is flooded, Raptor is runaway mine etc.).
That's at least some sort of plan. Sure it would cost quite a lot to implement but as the saying goes you have to spend money to make money. Dreamworld sorely needs new attractions to bring people into the park and in general needs a really good tidy up.
Yes I also realise I have completely forgotten WWW.