I plan on pick up snow tire/wheel combos for the MDX soon, probably from tire rack. The stock wheels are 19" and stepping down to 17" and getting a tire/wheel combo is the same price as just getting the 19" tires. It then saves having to have them swapped and rebalanced every time they are swapped. Won't look as nice but it's only a couple months during the winter. I plan on doing the same thing when I get my new car.
We had a lot of snow last winter and I didn't have any problem with my all-seasons on the Tahoe or Subaru but I don't want to risk it now with the little one on board.