This is a complex issue. SA's power is privatised so it's up to a private company to build a new power station. I think it is unlikely you'll find a company willing to invest huge amounts of capital in a power station that's only to supply power for air conditioners one week a year.
The 2016 power crisis in Tasmania was caused by low rainfall, Hydro Tasmania's management practices in the lead up and the failure of the Basslink interconnector power cable between the Latrobe Valley and Tasmania. Interestingly I don't recall any national outrage over the situation, eg calls to duplicate Basslink, build a new base-load power station in Tasmania or tow an iceberg up from Antarctica.
Another issue is the surplus base load resulting from the downturn in manufacturing in Australia, eg no auto manufacturing and closure of Point Henry aluminium smelter. In the Point Henry case, the nearby Anglesea power station was closed but this only supplied 40% of Point Henry's needs, the rest came from Loy Yang A which is still running. Hazelwood isn't being closed down by the State government. It's being closed by its owners as they couldn't sell it and have deemed it uneconomic to run a 50+ year-old power station in a surplus market.
Also there have been suggestions of market manipulation, similar to Enron's practices in California in the early 2000s. Here's one example:http://www.abc.net.au/news/2016-08-18/alleged-price-gouging-at-work-in-sa-elecricity-market/7763164
Sydney (at the moment) and Melbourne implement load shedding, and resultant rolling blackouts, during periods of extreme heat. In Melbourne arrangements have been made with large consumers to suspend supply or use their standby generators, with the mains as a backup, during these periods. I don't know if Sydney has similar arrangements.
Snowy Hydro's website states:
"Three of the six generating units at Tumut 3 Power Station also have large pumps that can be used to pump water from Jounama Pondage back up into Talbingo Reservoir, thereby ‘recycling’ water. Water cannot be pumped any further uphill than Talbingo Reservoir."
This is done at off-peak power rates.
'Gold-plating' of the network is a national problem. The industry has largely been privatised (fortunately not Snowy Hydro or Hydro Tasmania yet) so it is hard to see exactly what governments can do about it. Although the privatisation has been carried out by State governments, it was certainly encouraged by the Federal government.