That would be a tough move, I'd hang onto your M3 if you can. Your wife is probably happy driving the SUV, daddy's gotta be happy too. Although, with a kid in tow, the e90 is definitely more convenient.
If I were in your shoes and only needed one car for the family, I'd look into the new Audi RS4 Avant. All wheel drive for your snowy winters and performance for dad. Anyway, sorry I'm just thinking off the top of my head.
Congrats on becoming a father and best of luck!
