We did similar, flew into NY and out of Boston took the train to Boston then picked up car from there.
For scenery a couple of days based in North Conway – Horrible place basically one long row of shops but cheap motels and next to the White Mountains/Mount Washington, Drive the Kancamagus Highway, Flume Gorge/ Franconia Notch all nearby, as above the foliage should be impressive at that time of year.
For Coastline Maine will tick all the boxes, visit some of the lighthouses and eat loads of seafood.
To the south of Boston Cape Cod is very nice as is Provincetown. The Mansions in Newport are nice and you can do a cliff walk around the back of some although only worth a day visit IMO.
Alternatively just drive up though New Hampshire, Vermont and Maine and see what you find, accommodation will be plentiful and cheap (outside main cities)
edit: The area around Dartmouth College is rather nice.