Thanks for this.
We are happy to drive through the Pennsylvania Dutch area for the scenery. As you say, while the Amish are inevitably somewhat of a novelty to us as tourists, we would have no interest in stopping to take photos of/with them or anything of that sort.
Interesting that you say Harpers Ferry is a historic destination - perhaps this is why it was suggested to us so often. If this is the case, we may consider swapping it out for something else in the Washington area.
Rockport MA was also mentioned a couple of times, and given what you say about the I-95 situation near Mystic / Cape Cod, I believe this looks like a great alternative in a quieter area.
I like the shape this itinerary is taking already.