The Normandy beaches and the American Cemetery at Colleville-sur-Mer are astonishing, moving things to see, but I wouldn't go in winter, nor for just a few hours. When you have time you should see Bayeux and Caen as well, especially if you're a student of the D-Day actions.

I would probably just stick around Paris myself as well. If you're determined to do a day trip out of town, I wouldn't do Brux necessarily, but how about Brugge? Quick trip, great architecture, pretty charming.