You'll have to check, but most of the markets will close on the 23rd this year since Christmas day is a Friday. And public transit will be limited on the 24th, so if you're using that to change locations you need to consider that also. The decorations will be up, but the booths won't be open or manned, so it's not a total waste to wander the towns. The "vibe" on the 24th will be to shop in the morning and get home by noon (for the locals). By 1400 the streets should be empty of everyone but tourists.
I know everyone loves the little towns south and west of Strasbourg, but in December they're not my favorites. Consider Haguenau; close, easy to reach by train, nice old city center, and they do a nice display of lights. And even further north is Wissembourg, also reachable by train from Strasbourg, which is a perennial favorite with European tourists.
Note that it has not been a "white Christmas" in that area in years, but it is usually cold (20f), windy, and the days are short.