I would drive. It takes me under 6 hours to get from Philly to southern NH. It would take that long to get to the airport, clear security, fly, get luggage and car, etc.

Acadia is 10-11 hours from Philly. Save if for when you have more time. 3 days is not enough for that long of a drive IMO.

Skip the Cape...many things are closed that time of year.

I would do NH and Southern Maine OR head out to western Mass and the Berkshires, but then your hubby won't get "coastal".

My first instinct says Portland Maine. Portland is a great city and you could visit the other lovely town along the coast.

You could do Portsmouth NH as a base and stay at Wentworth By The Sea...not a B&B, but a beautiful hotel.

More later...

Going from Phila. in only 3 days, I would focus on Southern Maine -- Portland is the perfect city to visit -- lots of good places to eat. We drove from NYC to Portland in mid-June and it was close to 6 hours without hitting any major back ups or any accidents. You can explore from Portland. Or spend a night in lower Maine, perhaps Ogquint and then spend a day or two in Portland. Kennebunkport is also nice. Depending up when in October may determine whats still open in terms of lobster shacks and the likes.

Alternately if you fly to Boston and go from there u would save many many hours of driving and could see more of the coast.

The Berkshires or the Hudson Valley are both lovely and closer, but no coast obviously.

Portland is considered the foodiest city in America. I third the suggestion. You can get trail maps for wine, cheese, ice cream etc from each state and those ideas may help you plot a route.
More ideas can be found on chowhound.com. Go to the northern New England section. I also agree that a route thru the Berkshires would be nicer than going I95 all the way. If you can make it to Brattleboro, VT in time for lunch there is a great farmers market on Sat where several vendors sell ethnic meals or you can go to the Humble Kitchen food truck in downtown for bahn mi sandwiches. (see their facebook page). From there, head to Concord NH. It will be a state hwy not interstate so you'll see plenty of leaves. In Hillsborough NH there's German John's Bakery. From Rt 202, take Rt 127 to Contoocook and then Rt 103 thru small towns to Concord NH. Watch for the sign to Gould Hill Orchard in Contookcook where they grow heirloom apples. Continue on Rt 103 to downtown Concord. Bread and Chocolate Bakery is across the street from the food coop. Granite State Chocolate on Warren St makes their own ice cream or you can head up Loudon Rd to Arnie's where they also make their own ice cream. Connect with Rt 4 to the seacoast. You can make a detour for a wine tasting at Flagg Hill Winery.
Take the foodie tour in Portland. You can have a late lunch at Duckfat, famous for their fries. Lots of restaurant choices. We're more familier with the lobster shacks further north.
Have breakfast in Portland. Stop at Stonewall Kitchens and When Pigs Fly bakery on Rt 1 before you get to the Kittery Outlet Malls. (lots of free tastings) Have lunch at Petey's in Rye NH. Drive along the coast.
Whatever you do, don't take the Mass Turnpike. It's the dreariest limited access hwy in the state and you would be heading west looking into the sun on your way home.

If you're going to Maine and are a serious foodie looking for break-the-bank splendor, consider dining at Arrow's (Ogunquit) or (reportedly, as I haven't actually been) the White Barn Inn (Kennebunkport). Dress better than jeans and t-shirt, as last I remember both have a minimum dress code, and consider making a reservation.

Will second the recommendations for Portland you're getting thus far -- Portland is an excellent food town. Portsmouth, NH has some good food choices as well.

An excellent breakfast choice in Portland is Becky's. I also like the Maine Diner in Wells.