Everyone treats the situation a little different, I guess. I am going on 59 yrs old. I am planning to retire in 2016. Then I am going to push my '55 off a cliff. It deserves eternal rest after what I have put it through these past 30 plus years.
My car has been driven daily since 1981, 60 miles a day (or more), 5 days a week, year after year, thru the four seasons regardless of rain, sleet or snow/ice, and has taken me on a few long trips covering several hundred miles at a time. It has served me pretty faithfully.
The past three years in a row I have needed to cut out and patch rust holes in the inner rockers, outer rockers and rear quarters. Otherwise, everything else under the car looks like new still. The patching hasn't cost me anything except for my time. I got everything in the garage I need for metal cutting welding, finishing and painting. Beyond that, other repairs like carb rebuilding, generator repair, fuel pump replacement, radiator flushing, oil changes, etc, I can do in my sleep, so its not that expensive to keep it going.
It is a matter of economics to me. This car has earned a fortune for me thru the years and I haven't needed to sink a lot back in to it to keep it going. You probably couldn't sell it for what it would cost you in the tax payments alone for a newer car. Its cheaper to keep her. And I just run it year round. The car likes it better. Leave it sit for longer than a week and it probably won't start right up without charging the battery, the trans and pinion seals shrink up leaving oil slicks under the car, etc.
Winter is no deterrent for me. My junker can be seen flying down the highway any nasty winter day along with the rest of the poor fools in the rat race.