I would ditch the idea of spending time on the Riviera. You're lucky to get temperatures much above 60 around that time of year; I would rather come back when you can fully enjoy everything the area has to offer.

Winters, though, to tend to be a little milder on the continent than you would typically find here in Chicago, which makes sightseeing a little more palatable. Sounds like you've got about 8 days, which would be a perfect amount of time to do a lazy trip to Prague and Vienna. I don't see a reason why you couldn't get both your wishes -- get out and explore a bit during the day, then cozy up by a fire somewhere and have a quiet evening in.

Are there types of activities that you and your wife enjoy? Might help to tailor recommendations a bit.