Welcome to GenVibe!
The Vibe has been a highly reliable vehicle (as is the Corolla it's based on). Many people have had their cars 350,000 km (215k+ miles).
I've read a few people have experienced -10c to -20c in a Vibe and it's worked very well. Just keep the cooling system maintained and it shouldn't be a problem. An engine block and transmission heater would be a good idea.
I think Vibes are tough, but mine hasn't spent much time on gravel roads. I've experienced snow up to 5 inches, and it does fine, but beyond that not so great. The Vibe doesn't have much Torque down low in the RPM's, so it's not able to plow snow very well.
The body panels are made of the same materials as the Bonneville. However, you can get it in two-tone, where the lower plastic bits aren't painted. That way there's no paint to sandblast off.
There is lots of space between the 16" wheels and the calipers, even more on the 17" wheels
One problem with running Vibes in to high miles is that the Odometer stops at 299,999. Most people track the mileage manually using the trip OD's after that point.