I used to live in Brookline before moving downtown, I had a car and to me it was worth it, but parking can be a pain. In Brookline there is no on-street overnight parking allowed, so you'll have to pay for a monthly offstreet spot, which will probably run around $150 a month. Might be able to find cheaper, but that is about the norm, at least for Brookline. In Cambridge street parking will be a pain depending on the area, so you might want to consider a spot as well.