They may increase the capability of the ADF (if enough crew can be found), but there could be financial issues and political backlash.
Also, the only wars I can definitely see Australia getting involved in in the next 20 years are actions against jihadist terrorist groups in the Middle East, where SSNs wouldn't be able to do much.
There's a possibility that the ceasefire in Korea will be broken, but I believe that Collins and/or Barracuda submarines would be perfectly capable of taking out the KPN's Foxtrots, especially when you consider that the RKN and USN would probably each be deployed with larger forces - the RKN would be defending their home soil, and the USN has a larger force. The ADF would probably keep some forces in reserve ( for example, as far as I know, we only ever have a single fighter/attack squadron deployed over seas at one time).
Don't quote me on any of this, though, I'm merely a cadet
