You seem to be factoring in a near 20% depreciation in the value of the USD.
From its low point in late 2001, the AUD has appreciated almost 40% in value against the USD, whilst the USD has depreciated in value by between 25 -30% across a broad range of currencies (except, the Yen).
Going forward, the same super-charged economic atmosphere that benefited Australia whilst the AUD fell could well advantage the Americans as the USD falls further.
Of course, critics would argue that the US would still be uncompetitive vis-a-vis China and various of the Asian Tigers. More likely, however, with a variety of Asian currencies tied to the USD, and with their own internal problems (ie: SARS, internal demographic dislocation, growing unemployment, inefficient State enterprises in China, and an over reliance on manufacturing, etc), countries such as China could well suffer a reversal of economic fortunes. Going forward, I would expect South Korea, and Japan to start benefitting from some of this re-alignment (South Korea, in particular).
All of this means that equilibrium will fall far short of what you are surmising, as the self-fulfilling prophecy that would have you achieve a AUD 875 dollar price for gold will also result in Australia having an unsustainable CAD, a declining international competitiveness position, and a rising interest rate regime.
In turn, these factors alone will lead to the AUD falling back against the Greenback such that mid- and long-term equilibrium will, more likely, be achieve in a sub-70 trading band. Already, the AUD has ridden hard, not on the basis of fundamentals, but on the basis of speculation, high real interest rate returns, and as a means of profiteering.
The next 3 months should be very interesting for the AUD as, short term it will spike to 69, before falling back to near 60 (by mid-July), and then stablising in a 62 -66 trading range.
80c has not been seen since well before the days of a free floating exchange rate.
