We will be heading from Mystic, CT to a final destination of Mount Desert Island/Acadia for the 5 days after Labor Day.

Any suggestions on places to stay and a halfway point for the drive?

For the half-way point, we are thinking of the York Inn or somewhere in Camden.

For Mount Desert, we are thinking of the Bar Harbor Inn, the Blue Nose Inn or the Asticou.

Any other ideas? We would prefer not to stay in a small B&B.

Are you referring to the York Harbor Inn? I am not familiar with the York Inn, but I've driven by York Harbor Inn many times and it looks nice. However, we prefer the Black Point Inn in Prouts Neck and The Inn by the Sea in Cape Elizabeth.

We stayed two nights at Boothbay and took a cruise to Monhegan Island before going on to Bar Harbor. We just loved Boothbay. We stayed at the Fisherman's Wharf and were very pleased with the service/ location of that hotel. Maybe, another option to consider instead of Camden.
I like your choices of the hotels your considering for Mount Desert. We stayed at the Wonderview and weren't too pleased. I did see those hotels and wished I had stayed there instead.

What about the Wiggins in Booth Bay?

I have been going to Inn by the Sea in Cape Elizabeth for 13 years. Black Point Inn is lovely - or even lovelier- but you can not go wrong either way.

I'll second the Black Point Inn at Prout's Neck in Scarborough! Try to get a room in a detached building that might offer more privacy. Portland is nearby and fun to explore.