You are underestimating the car mileage via Hartford. It's at least 220
miles. And if you follow the Shoreline Train Route, it is even longer.
Unless there have been drastic changes in trackage, the train route from
Boston is through Rhode Island and then along the Connecticut shoreline.
Again, the Acela is even slower than it should be because of crappy
trackage and too many stops, although the tracks are better in that part
of NY/NEw England than from DC to Florida.
Personally, I'd rather travel by boat.
It's a nice boat ride through LI Sound and then up to Boston.
When I was a kid, though, I was on the train at least once a month from
New Haven to Back Bay Station to visit grandparents and aunts and uncles
and cousins. It was a great train ride back then. At least once, I had
to navigate myself from Back Bay to Maverick Station to get to Revere
Beach via the BEYr streetcar line. My paternal grandparents lived there.
I was probably 11 years old at the time. Great adventure.