I also have to agree that you can't do it all in one week unless you don't mind spending a lot of time in the car.
I grew up in Salem, so I have to argue with the person that said there isn't that much to do there!! There's lots to do. But if you don't want historic things, then maybe not for you. If you are in the area though, everyone should visit at least once and learn about the witch trials.
I have family on Mt Desert Island so we go up there often. (About 6 hours from Salem, less if you have a lead foot

). Acadia is wonderful. If you're looking for beautiful scenery, this is a must-do.
I've never been to the Cape even though I've lived in MA my whole life because I've just been too intimidated by the traffic. If you avoid Labor Day weekend proper you should be okay.
Even if you don't want to do the historic things in Boston, don't discount it completely. There are lots of wonderful places to eat and if you like the arts, lots to offer there. But again, the Bull and Finch might not be what your husband thinks it is. There are lots of options for harbor cruises if that's what interests you.
As far as the Boston traffic with returning students: you don't want to be driving in Boston anyway! That day you should be using public transportation. There's never a good place to park in Boston and it's really pricey. The T is a much better option.
Another place that offers whale watches is Gloucester, MA.