I did exactly that. The surveyor's evaluation puts me about $50,000 ahead...plus I get to sail the Sea of Cortez, brilliant, and then I can sail home via Bora Bora...priceless!
The process of buying a US flagged boat is simple. The transfer of registration to Oz is equally painless. The cost of import is based upon purchase price, not Oz valuation (as long as you get the boat home in a reasonable time frame), and the cost of getting it home (freight) can be factored into the equation to further reduce the final import cost.
"if at first you don't succeed....Redefine success"!