Sorry, I only just caught this thread...
Seeing as they are saying Bourke will be flooded with major to moderate flooding until mid March, I should think that you might want to reconsider your timing for your trip. I see that Bourke is only just now getting the first of the flood waters from the first rain event in Queensland. They've had our water from the rain event before Christmas in January and they are yet to get the second peak from Queensland.
The talk out here is that our "wet season" is not over yet, we are just in the early days of February and if the weather pattern is anything to go by, we're still due for more rain.
I'd advise to hold on your Darling river trip, as it is not just going down the Darling river that could be difficult for you but also getting out there as well. As most, if not all roads out around the Darling are of black soil, if they are at all wet, they are the worst kind of road to drive on. It also doesn't take much rain to see Shire councils shut them down either, these days. Our outback Shire's are at best, broke and they can't afford too much in the way of road fixing. Some of them, if not all, will be awaiting for flood relief money to come in before they actually do anything about the roads out here. We're still waiting for the main road into town to be fixed from flood damage that occurred back in early December!
If you can plan it for the September school holidays you might by then have a better idea of how wet or dry it will be.