I get sucked in each time this comes up so I priced another itinerary I'm looking at. ARN-SYD//DPS-ARN, two people in business class.
Air Canada had some options available requiring an overnight stop in Dubai on SK/SQ/EK.
Buying the points (at 80% bonus), plus taxes, plus value of the miles I wouldn't earn comes to $14,010 aussie (plus overnight DXB hotel).
Purchasing a fare (TG/TK) comes to $12,144 aussie.
I'm sure there are some bargains to be had but do your homework, consider possible devaluation, interest on the money, less freedom of redemptions. But then again Air Canada redemptions can throw some interesting airlines into the mix that you wouldn't otherwise take.