Lets cut to the chase.
The problem with the MDB is politics.
This government has neither the will nor the capability to respond to the mess created by the states.
Water is massively overallocated in Qld and NSW. Even now water is available unmetered in Qld (eg around Charters Towers).

Vic plans to take minimum 75 Gigs to Melbourne via the NS pipeline from the Goulbourn. Who knows what has already come out via the Goldfields superpipe to Bendigo and Ballarat. (That info is hard to get!)

SA doesn't want to build the Wellington weir and open the Goolwa Barrages even though at 8500 Ha the lower lakes evaporate 1700 gigs annually. To put that issue into perspective rainfall over the MDB may-Aug was around 940 gigs. Evaporation on he lower lakes Nov- Feb will be 770 gigs.....if they were full. (admittedly not all 85000 ha is currently wet but you get my drift)
Irrigators have a contract with the states to supply water. They paid for it. Under contract law thats called consideration. To sell it to a higher bidder (or swap it for votes) doesn't extinguish in my opinion, the rights of farmers to the water promised them. If they don't get it they need proper compensation.
Proper compensation. So lets get rid of the notion of willing sellers. Desperate people are not willing sellers. nor are those forced to sell water they werenever going to recieve anyway.
Lets fix the MDB.
Properly.
Lets start withn the Western Rim proposal on the lower lakes, build dams (in spite of the ALP/Greens No Dams policy) return water to irrigators, and review water grants over the last 8 years in QLD and NSW..with a view to returning that water to the basin tha should never have been granted anyway!

In my opinion, it is all about carefully-targetted compulsory acquisition and appropriate compensation. There is no way that purchase from willing sellers are going to resolve the problem.

Personally I am opposed to the construction of any new dams, unless they are deep profile and specifically constructed to replace existing shallow impoundments: which would be breached and decommissioned.