The heart of Old Sturbridge Village is a re-created New England town of the 1830s (so, technically not the colonial period), using authentic buildings that were rescued and transported to the site. It's a wonderful complement to a visit to Plimoth Plantation, where it's always the 1630s -- how much the country had changed in 200 years! It's right off the Mass Turnpike, on the way back from Vermont towards either Boston or Cape Cod.

Thanks for all the suggestions. We'll be sure to repay with a little travel report. The reason for Concord/Lowell is that as a historian I just have to see the home of Emerson and Thoreau and the birthplace of America's industrial revolution. Sturbridge would interest me in terms of how history is recreated in a non-academic context. Rather expensive though, I've heard.
One more question: we read about a restaurant, The Creamery, at Canterbury Shaker Village that sounds interesting. Can anyone recommend it?

The Creamery has been replaced by a new restaurant called The Shaker Table. Here's a link to the menu and info about the new chef.
http://www.shakers.org/restaurant/index.php?show=LUNCH

Adult admission to either Plimoth Plantation or Old Sturbridge Village will run about $20 without any discounts (student, AAA, senior citizen, etc.). Both opreations involve many buildings, staff, and acres of grounds; those prices are heavily subisidized.

Depending on your interests, you could easily spend a whole day in Concord - I could spend more. It has the battlefield, cemetary and multiple houses open for tours. We also spent a few hours at Walden Pond.

when you are in Lowell, if you are looking for lunch, consider the Southeast Asian restaurant (really, that's the name of it, not just the description). Terrific Vietnamese and Cambodian food. Very, very spicy!

I loved hiking Mt. Washington last summer, & my family & I stayed at Purity Spring Resort in Madison, NH. It was about an hour drive to Mt. Washington but so worth the stay. They're family owned, off the beaten path, just quaint & quiet. Work that in if you can! Have fun!

Have a wonderful time. If you are serious about getting all the way out to the Berkshires, spend a night or two in Williamstown, MA. There are three wonderful, small, art museums within a 20 minute drive (Williams College Museum of Art, the Clark Art Institute and MassMOCA), there is some good hiking (check the Williams Outing Club website for suggestions) and there are a number of good hotels and restaurants in the area as well.

Late September is early for leaf-peeping in the area, but it is still beautiful and still warm enough for some good hiking (by late September the Lakes Region/White Mountain area of New Hampshire gets very cold and hiking in the Whites that time of year is very dangerous if you are not prepared for sudden drops in temperature).

The College will be in session, but the parents should be long gone, making Williamstown a classic New England college town. It's not really "touristy" but there is an infrastructure to care for visitors with high expectations.

You have picked a lovely time of the year to visit. I love your note about eating your way through the CI's restaurants. To the consternation of friends, we have been known to drive from RI yearly just to dine at the Essex Inn outside of Burlington. Expensive - yes, but so worth it for a "foodie". Another good eating spot are the restaurants in Manchester, VT, and of course, all the lobster/clam shacks along the northern MA, NH, and ME coasts.
Have a great trip!