The people building the capital will make a profit over the year, so consumers will make up for the 0s with higher prices when there is not enough energy. And over the long term $0 prices potentially lead to building less infrastructure leading to blackouts.
Basically we know the average price is not going to be 0. Therefore, 0 prices signals variance. Variance is pretty much always risky and expensive in big infrastructure; and the electricity market is a good example. It can hopefully be managed to only be a minor inconvenience but it is certainly not a positive for anyone.
It does signal that there is a golden window to, eg, run a desalination plant. If anyone takes advantage of that opportunity then it would be a win, but the symptom of that happening would be non-0 prices.
EDIT
Also, coal plant failures in hot weather are probably a symptom of them not being maintained. Australia has already seen a Labor-Green coalition in federal politics; you'd have to be an idiot to spend money maintaining a coal plant in that political environment. Better to let them run down and try to extract money from the government in a crisis situation which seems to be the current strategy.