Well, if I were you and had the time, and had not been there before, I would spend at least a day in Boston. I find that the information centers are great and can steer you in the right direction if you tell them your interests. Can save a lot of time a $.
You might be traveling up to Surrey on Rte 1 once into ME if it is an hour from Acadia. On the coast I hope? If you travel Rte 1 there are great little places along the way (along with the factory outlets and LLBean) -- Boothbay Harbor, Kennebunk....
Well no matter how much time you have it probably won't be enough and you will want to go back.
A word about Red's Eats. It is very famous and must do for many visitors. It is a little shack at the bottom of a hill that anyone going thru Rte 1 has to pass thru, that serves seafood takeout. For years my husband and I have passed it, seen it on the cable food channels, read about it. There is always a looooong line of people. I decided we had to do it just once and so we did it this past trip. The lobster roll is $20, comes with no sides, but it contains probably 2 lobsters worth of lobster meat. We waited for 2 hours in line with many others first in the sun, then in rain. The lobster roll was the best I have ever had, but not sure I would stand there again for the experience.
I had been to Bar Harbor many years ago and was surprised to find that it has become quite the tourist destination, cruise ships dumping 6,000 at a time into town and all. If that is not your cup of tea I would spend more time in the park, and off the beaten path. There are many side streets with the names of "Bay View", "Old Harbor" etc. Following them can lead you to some great photo-ops. There is also fishing, boating, antiquing, etc.
No matter what, have a wonderful trip. I am sure you will.
Best, CS