I kept a Boxcar Willie for two years and it did fine until August and then died.

I have a holdover from last season, but the tomatoes are smaller and the plant is losing vigor. New ones seem to produce better.

If you like the Tomatoes they produce then keep them. I do not have hold overs but get Tomatoes that spring up on their own I guess from where tomatoes fell on the ground and rotted,

Mine often winter over, but they're never very productive. You might want to try taking cuttings, they're easy to root.

For those who have tried it, did you prune them back in the spring?

I prune off the dead stuff and just leave the vine and the green parts. The produce is smaller than that which comes from new plants. However, it comes at a time when we haven't had any produce for a few months, so we are still pretty happy to have them. It sounds like we aren't taking any big risks keeping them around, so I think we will continue to do so. We may also try the cutting method, which we haven't done previously.

Never had much luck overwintering my tomatoes. I prune them back and they get lots of green, but no tomatoes. By the end of the calendar year, not much is left, so I get rid of all of them.

Each spring, I dig under all of the grass clippings and add lots of coffee grounds, so any plants actually get in my way when I'm doing this.

You're right, no big risk in keeping them around, but personally, I don't bother.

My cherry tomatoes are smaller and less productive, also much less sweeter (Sungold) but it is actually better for me, last year they produced too much for single me heh