I've never found Acadia to bad as far as the bug thing. Usually at sunset the mosquitos but nothing a little bug spray or campfire smoke can't fix. We have camped at Seawall with the kids, rode the carriage trials on bikes, hiked may trails and there are a couple of beaches, kayaking, sailing, you name it. There are also some nice shops in Bar Harbour and there is always the mini golf, amusement type stuff off island which frankly we avoid.
Oh and don't forget to have popovers and tea at the Jordan Pond House. My kids like the popovers stuffed with ice cream and hot fudge sauce.