I took 2 extra flights last year, using web specials, for no other reason than to insure I got my Executive Platinum. It's probably easier for me being in Vancouver, CP's hub, and Toronto/Ottawa being more centrally located means you don't have as many choices for long routes.
My best deal last year was YVR-BOSton, for $299. This gave me 5028 qualifying miles. But because I made Platinum I got double points. As well, there were 3 different, cumulative, mileage bonuses on that route. The end result is that I ended up with just shy of 30,000 points for that trip. The irony is that many points will get you a business class seat from Vancouver to almost anywhere in N America.
One great thing about web specials is that you can find out if you can upgrade in both directions, before you even buy the ticket. Combine this with 1000 pts for paying by Amex, 500+ MR points, 500 pts for on-line booking, and 500 points for e-ticket, and you could end up with 32,000 miles for about $360, including taxes, as well as 5000+ status miles, and travel in business class. (BTW, that works out to about 1c per point.)
I'm not sure I would do this just of the points, but if you need status qualifying miles in a hurry, there's not better way.
Regards,
Ken Hamer