I think it's important to be able to run appropriate tires for winter use.
If your gonna be out in ice/snow/slush/muck then life will be better on purpose-built tires. If your current frame can accomodate them, then fine. Otherwise you might want to consider an MTB or 'cross bike. I have one of each for just such occasions. My road bike can (barely) take 700x28's, so it's my "fair weather" ride.
I'd also agree with earlier posters who pointed out that you've got some nice vintage components on your bike that will be hard or expensive to replace and felt that that was an important factor, too.