We have driven the past 4 or 5 times we went to WDW and will probably continue to drive down.
We're just NW of NYC and take 287 to the NY Tpke. and follow that and 95 all the way. 287 will drop you onto the turnpike around Perth Amboy and you'll miss all the Newark Airport and docks traffic.
The trip takes us about a day and a half or so stopping overnight in either North or South Carolina. Leaving early the first day and driving until about 7:00 and then getting an early start the second day, we've arived at WDW anywhere from noon to 3:00 the second day. Depending on where in Mass. you're coming from, you could add that to our time and figure on a full two days. Do NOT take 95 through NYC. If you're coming down 95 through Conn., get off at 287 at the NY line and take that to go around. If you're coming across 84, stay on that until you get to 87 in NY and then take that to 287.
Gas, tolls, and lodging will definitely total a lot less that airfare, even without the rental car. The only problem is the extra day or two on either side of your time at WDW, which is only a problem if your time is limited.
Having a car at WDW, especially if you're staying on site, is not critical, but it does make getting between resorts a lot easier for enjoying the resort dining, which is usually at least a notch above many of the park restaurants.