We did a September/October trip a couple of years ago. I'd always wanted to see New England in the fall, and it didn't disappoint one bit.
We spent a week in Newport, RI at Wyndham's Long Wharf and thought it was great. The grand homes were fascinating, and the beach towns with unbelievably good seafood like
https://www.rhodyoysters.com/ in Matanuck make us want to go back. The weather was great, but not a lot of fall color.
We loved Marriott's Custom House. It's very comfortable and in a fantastic location where you can walk and explore the history of Boston. The metro station is just down the street if you want to explore galleries and museums further afield. Boston definitely merits longer than a week.
Did another week in Smuggler's Notch and loved that as well. We hiked in the "mountains" (I'm a western girl, so they seemed like hills to me - but the fall colors were brilliant!), visited wineries and breweries, Shelburne Museum, Ben & Jerry's, Rock of Ages Granite Quarry, Lake Champlain, and just enjoyed exploring all the towns along the byways. I'm not a good photographer, but I made my husband stop all the time, just so I could get out of the car and gasp at how beautiful the multi-hued hills were!
Another week in the amazing top floor 3BR suite at Maine 84 in Kennebunk, ME. We did a lot of wandering the back roads trying to find the best lobster roll in Maine. We loved the coastline, were impressed by President Bush's compound, shopped for antiques, and walked the beaches. Driving through towns to us was like squirrels to a hunting dog - we always found something that caught our attention and made us stop to explore.
While we were in the area, we decided to drive up to Montreal (stayed in a B&B in Vieux Montreal), then wandered down (up?) the St Lawrence River road all around to Gaspe, then down to Prince Edward Island, back down to Campobello (one of FDR's homes), then back through Hyde Park (Teddy Roosevelt's home) to finish up our trip.
I can't wait to go back! Our next trip back east is to Hershey, PA, NYC, then on to Cape Cod.