Doesn't seem to be much data on .com.au sales, probably because of only recently being opened for sales...
I'm not sure how much of a reseller market has developed thus far in .com.au domains, DNSalePrice only shows 1 sale for instance. DW has one premium and one semi-premium letter in it, and the combination goes well. Austrialia has 21 million population which is roughly 2/3rd that of Canada. I'm guessing Austrialia has a higher take up of .com.au than Canada has of .ca though, so perhaps in the long run the same value as similar 2 letter .ca domains.
I'd hold on to it though - without the current reseller market the conditions aren't the best for a sale.