To me, the difficulty with reproducing a New England feel in TS3 is how regular the buildings are. I've never lived in New England, but I have a number of relatives in and around Boston, and have spent plenty of time in Maine (during the summers, thankfully; I'm not cut out for that kind of winter). Thinking about how sims buildings look, it's like they're all too new, too regular, or too perfectly made.
To me, New England houses and stores need to look like they've been there for a while, like they're weathered, even if they've been diligently cared for, like the wood has responded to the passage of time, bending and shrinking and drying out as it aged. Corners can lose their sharp edges, some of the buildings don't quite stand up straight, and nothing feels overly polished or smoothed out. A downtown area may have a row of buildings all pushed up against each other, but each one looks like its own character, completely distinct from its neighbors.
One other thing I haven't seen mentioned is the lighting. New England is so far north, the sunlight can feel kind of thin or washed out, even in the summer. A few years ago, my brother and I drove up Route 1 in Maine, just to have a look. (We got a couple of towns past Winter Harbor before turning around.) Even on a sunny day in August, it felt like there were always a couple of clouds dimming the light. One local mentioned how in winter, everyone's home by 3:30 because it's already dark outside. A lighting mod that reflects a far northern latitude might make a big difference in how one of these worlds feels as you're playing it.
Anyway, those are just the thoughts of a lifelong Californian who thinks New England is a wonderful place to visit any time of year that one jacket is enough.