Yes, I have dxed from nearby Boothbay, ME and had a similar experience. You get the salt water path, thanks to the geography, and many New England AM signals are directional toward the east/northeast (especially at night). So, lots of selection on AM there. Boston area stations come in well; go a few miles inland and they fade fast.
The geography there also enhances FM signals from southern ME/Portsmouth, NH thanks to topography where you're a few feet up on the rocks and the signal is all over water.
The difference between the mid-coast of Maine and the NC/SC coast is that the land terrain in the Carolinas is sandy and level and has great ground conductivity too. Almost as good as the salt water than surrounds it.
In Maine, it's basically a one-way street. Signals from the north don't come in nearly as well, passing over all that granite. This is why Cape Hatteras is such a terrific dxing spot for AM. It's good for FM too - when you get those humid days that make for good tropospheric enhancement. But you can get that effect in lots of coastal locations (Gulf Coast, SE New England, etc.) and it varies. The AM goodies, on the other hand, are pretty much always present.
New York to Florida all day. Hard to beat!