Newburyport is a scenic historic port city, small and pleasant for walking around. Portsmouth, New Hampshire, is similar and a little bigger, has a good restaurant scene but no rail stop; easier to take the bus from South Station bus terminal in Boston.

Salem has similar attractions to Newburyport and Portsmouth but also the very good Peabody Essex museum, good to have at hand if the weather makes walking around unpleasant.

Concord is small, historic, upscale. People usually drive because the sights are scattered but it's certainly possible to visit on the train from North Station.

Lowell, one of the many early 19th C industrial cities around New England that took off in similar fashion to Manchester, harnessing water power for textile mills, is the only one that's easy to visit. Lowell has a national heritage site that explains the industrial revolution from a social and technological viewpoint. Some nice walks and restaurants in Lowell too.

Portland, Maine is a long train ride from Boston North Station. Good destination for shops, strolling and dining but too far for a day trip.

Worcester is a good sized city at the end of one of the commuter rail lines but not a good candidate for walking around. There's nothing else really worthy of a stop on the way to Worcester either. Providence, in the state of Rhode Island, about the same distance as Worcester but much easier to visit on foot with plenty to do and see and a good dining scene.

None of these trips have scenery along the way to compare with the Hudson Line out of Grand Central, where you travel right along the beautiful Hudson River, but plenty of nice destinations.