You guys are cray for spraying them with the wheels on the car.. I don't see how that would be 'easier' or even save any time. Though from what everyone is saying they came out great (I can't see the pics!)..
I'll be spraying my winter set this weekend.
$40 a can!? Yikes. haha.
As far as durability - I only have a year as a reference, but I've seen a pal's last flawlessly for that long through many washes and miles. More than enough considering you can just peel and paint again!