I couldn't believe the $479 price for the big chainring, so I typed "dura-ace 7900 outer chainring" into Google and found everybody else seems to sell that between ~$150 and ~$250. Is all bike stuff incredibly expensive in Canada?

At any rate... If you want to replace the whole crankset, then go for it. It would help to know what you don't like about your current one though that had you considering a replacement even before the shifting troubles started.