Kevlar jeans are great, and they will keep the skin on your legs from being turned to hamburger. I've got a pair, love them.
A couple of things though: they are not quite as comfortable as regular jeans, and heavier, and more expensive - especially if you are talking about several pairs so you can wear them to work every day. Mine say to let them hang dry, so that can be an additional consideration.
You might want to consider a 4 season overpant. The jeans won't help with the "very cold" any more than regular jeans. With an overpant, without the liner they really don't add any heat in the summer, but with it in you can lower the temperature floor you feel is "riding weather". Plus most will have some type of minor armor padding to go along with the abrasion protection. And when you get to work you step out of them and underneath you've hopefully remembered to wear whatever you would normally wear to work.
Mine are not the best - the legs won't go over my boots, and the liner looks warm but kind of cheap - but @ $80 they were less than most kevlar jeans ($80-120). Most overpants seem to go from $100-$200. Note: most will recommend you go up a size for overpants, and I'd recommend trying a local store if possible, as fit just seems to vary widely.
It is not for everyone, but definitely an option.
