Whether you need a car or not depends entirely on where you live and what your needs are. In your case, you probably want to sell it, since both of you will be able to walk to work and to many shops and have easy T access--which sucks right now, but not as much as driving does. The argument for keeping the car is that you might want to do some large shopping trips, or trips to places that are annoying or impossible to get to via T (e.g. Ikea, Costco, or a weekend in western mass or Maine or even the Cape). But given how expensive parking is, and how convenient the rest of your transit needs are, it probably isn't worth keeping the car just for those.