Can't help much on the coastal route but I've spent alot of time in Western Me (Kingfield/Rangley area) and it's beautiful country.If you don't want to ride the coast on the way home it's a nice alternative. Not so many people. Rt 4 from Farmington to Rangley, or 4 to 27 to up thru kingfield, carrabasit, stratton to rangley, both eventually to rt 16 over to NH. Gotta stop at LL Cote's in Errol NH for everything sporting goods. Like LL Bean and Kittery trading post combined. From there you work your way south/west to rt 3 to 93 or just stay on 16. 26 over to Colebrook NH brings you thru Dixville notch, pretty.
If your wanting to stay just a bit lower, go rt 2 in Me out through Bethel, grab 113 down through the national forest to 153, then to 16 (about mid NH). from 16 you can go all the way back to 95 if you want. Or, if you swing far west enough, you can go down 84 from western ma, down through Hartford CT into Pa. 84 down through S/W CT and NY into PA has some nice views and elevations. I tend to go where there are less people and traffic. You'll be sharing those western me roads with a couple tourist and logging trucks. I don't know if that means it's off your list or on, but it's a pretty part of New England. Deer, bears, and moose, so be on the lookout. Moose are the worst as far as seeing them after dark.