I wanted to note that my niece told me once that the Massachusetts accent is the ONLY one that gets more pronounced in the UPPER class. Most get worse in the lower class! I did not know that!
I've lived here my whole life and I would disagree, though I suppose it depends on what you mean by "upper class." What I think of as upper class (Yankees, Brahmins) may drop some Rs but they have a pretty measured way of speaking. The strongest accents are, in fact, much more pronounced in the "lower class" (i.e. poor) neighborhoods/towns.
John Kerry has a New England accent, but he doesn't sound like one of the SNL Boston characters (who do sound like that).