yeah, if you're getting your car in March, I wouldn't install winter tires for this year, it's too late. The general rule of thumb is, if temperatures are consistantly below 40 degrees daily, then it's time for winter tires.
This is the first year I installed snow tires. Prior to this, I've always used all-season tires during winter time. It's impossible for me to gauge how much better snow tires are vs all-seasons, since it hasn't really snowed this year in DC.
I think 2 weeks ago, there was sleet and some (1/2 inch?) accumulation on the ground, my snow tires handled it like a champ, but my old all-seasons would have no issues either.
March is actually a good time to start looking for winter tires for the next winter season. Alot of new and used tires out there for sale.