Well, I think it is you who is showing a lack of understanding....

Well, I think it is you who is showing a lack of understanding. You claim that the SA blackout was a grid failure, supply sources were irrelevant. But supply sources are very relevant to grid failure, because variable or unreliable supply sources stress a grid and make it more likely to fail. Let's have a look at some of your points:
-- a costly coal plant had closed due to inability to turn a profit -- That lack of baseload power was a factor in the collapse of the grid. And a cause of the inability to turn a profit was the mandating of renewable energy; if renewables had been competing on a level playing field then the coal would have remained viable. BTW, two coal stations closed - the only two coal stations - and there were concerns then that it would cause the collapse of SA's system. It took only 5 months! See here
-- a gas 'peak' generator was unexpectedly mothballed as the ongoing power cost decrease due to wind made in uneconomic -- That's more of the same. The gas plant closed, not for genuine economic or performance reasons, but because renewables were given the inside running. It's pretty hard to compete wih that.
-- $9000/MWh was available to all power supply companies as it was a spot market price. Any gas generator could have sold at that price -- SA only has two significant CC gas plants that might have been able to step in fast enough, Osborne and Pelican Point. With one down at the time (?), that doesn't leave a lot to choose from.
-- the reality is wind power is delivering cheaper, pollution free power to SA routinely -- Now that is complete garbage. SA is the most expensive state for electricity by far. And the stupid obsession with renewables is the primary cause.
"On Christmas Day, according to the average price tables published by the Australian Energy Market Operator (AEMO), the Regional Reference Price (average spot price) for a megawatt hour of electricity in South Australia was $91.67.
The corresponding prices in New South Wales, Victoria and Queensland were $37.33, $20.38 and $36.20.
The average daily spot price for a megawatt hour of electricity in December 2015 was $62.19 in South Australia, $43.37 in New South Wales, $46.84 in Victoria and $42.08 in Queensland.
On December 17, the average spot price for a megawatt hour of electricity in South Australia was $259.59, while on December 26 it was only $5.06.
It is clear that South Australia has the most expensive and most variable power on the eastern states grid.
The reason for the high (and extremely variable) price of electricity in South Australia is our very high dependence on solar and wind generation compared with the other states.
This results from the rapid expansion of renewable energy generation in South Australia.
According to a Deloitte Access Economics study recently released by the Energy Supply Association of Australia, South Australia’s solar and wind generation capacity per head of population is already more than three times that of any other state or territory.
[..]". See here.
Germany and Denmark have the two highest electricity prices in Europe, and guess what - they have the highest proportion of renewables.

SA's grid was destroyed by an obsession with renewables, not by the storm. The storm simply provided the final nudge to the inevitable collapse. Without the storm, the system would simply have collapsed a bit later on. It wouldn't have taken long, after all it's only 5 months since the last coal plant closed.