Other than the exchange risk, one more thing to consider is interest rate risk and the returns you are generating from your money. If it is lying around in a current account with no interest then it is rational to keep it where you intend to stay(US or AUS).
Now if your money is working for you, earning interest or has been invested in the market then it seems reasonable that you should put it where it earns the maximum for you. But that comes with a rider, the exchange risk you may have to bear if you are converting between the currencies. Do the returns earned by your money cancel out the FX rates moving up and down and still leave you with a positive return, compared with what you would earn if your money was where you stayed. Consider the below scenarios
Stay in US -> Money in AUS -> Check what are your returns
Stay in US -> Money in US -> Check what are your returns
Stay in AUS -> Money in US -> Check what are your returns
Stay in AUS -> Money in AUS -> Check what are your returns
Do evaluate all your options before you transfer your money.