Something to keep in mind: Acadia National Park can get extremely crowded in the summertime. A few weeks ago, a new record was set when an estimated 35,000 people visited on a single day. The good news is that you don't need to drive to Mount Desert Island to see Acadia National Park; you can go to Schoodic Point or, with some careful planning, to Isle au Haut. (Look at a map to see how the park is broken up into three distinct pieces.) But realize that in July and August pretty much all of Downeast Maine gets crowded.
Also, I volunteer on the 470 project in Ellsworth. It's a fascinating undertaking, although right now there isn't much to see other than a lot of dismantled pieces. But you're welcome to stop by on almost any Saturday--and there's always the Downeast Scenic RR train to ride.