Hi PJ! Here's a few suggestions. These are mostly close to Route 1 with a side trip to Boothbay Harbor and Castine.
Bug Light in Portland for a great view of the Harbor.
Take the trip down Route 24 from Brunswick, a penisula with a wide assortment of caches. Lobster Stew and a frosty at Cook's is recommended.
At Boothbay, all of the Pike Patrol BRLT caches are terrific. Don't miss Hasta La Vista Maybe. Encylopaedia Botanica is in the Maine Botanical Gardens, small fee but beautiful place.
Rockland, there's a cache at the start of the mile long Breakwater, then walk on out. Hot Dogs at Wasses, none better. Then a 15 minute hike up the Beech Hill cache, best view of Penobscot Bay in the area.
Camden, you drive to the top of Mt Battie to get Patty's Mount Battie cache. Great view if the fog is not in. Down at the Harbor, Schooners R us cache (mine) will put you harborside. On Saturdays and early Sunday mornings the schooners will be in. Try lunch at Cappy's chowder house, best Bloody Mary's in Maine! There's a real cool earthcache slightly out of you way called Gravity Outlaw. If you want to see some spectacular mansions and beautiful little park, do Going to the Chapel.
Just north of Belfast, going into Moose Point and take the 15 minute walk along the shore to the one cache there. Small fee but worth it.
Fort Point cache in Stockton Springs. Now you're getting "downeast!"
Now you need to decide about side trips. Castine has a lot of nice caches. The Witherle Woods caches are some of my favorites.
Acadia National Park is Maine's only National Park and there are plenty of opportunites, but generally a rather busy place in summer months.
If you're continuing on Route 1, Roque Rocks cache is worth a stop and you'll be rewarded with scenic vistas all the way to the cache. You need to go when the tide is on the low side. This is one of the few 2001 placed caches left in Maine.
From there, you're on you own as that's a far downeast as I've cached. Have fun!
Sometimes the road less traveled is less traveled for a reason.