JB, I've looked at the Grafton Loop trail and it has just about every sort of criteria I'm looking for- loop, option of more miles, or less miles, easy access. How would you rate the difficulty of the hike? If the hike is normally a very strenuous hike the addition of snow might make things somewhat undesireable. Maybe, as an option, there's something closer to the coast that may not be as snow-prone. I'd like to have a couple of alternative plans and make the final decision at the last minute depending on weather, conditions, etc. Thanks.
Sorry, I didn't read the response directed towards me before posting.
I think that "closer" to the coast really limits you in the fact that you can't get multiple days out of it. I think that the 20 miles of one of the loops, over 4-5 days would be fantastic.
Again, you'll have the "big payoff" of the rough peak, but I think that with your slotted time you can have luxurious meals, spend a rainy afternoon playing cribbage in a shelter, and not have to worry about rushing. My father is 60 years old, is in decent shape, but has never backpacked, and I would definitely take him on such a hike with that much time alloted.
Another suggestion, and I've only hiked a portion of it (and I was fogged in to about 15 feet of visibility) is the Bold Coast Trail. Give it a google; local papers, the NYT and other sites have reviews. It's in downeast maine, waaaay past Acadia, (probably 4 hours from Portland) and is a 10-12 mile loop with primitive campsites on the ocean. The sites are FCFS, but it is beautiful and unlike any other hike. No mountains, but not super easy.
You could also consider hiking/camping in the Mt. Blue region. There's no multi-night looping, per say, but you could camp in the State Park and drive very short distances to some beautiful peaks. Tumbledown et. al. aren't as prestigious, altitude wise, but it's like being 5'8" in a family of five-footers; it's all about perspective!
Let me know if you have any other questions!