Ferry across Bahia de Samana

Your guess is correct.

A North-Eastern route from the North Coast to Bavaro would be highly desirable. But the national park will stop any highway from being built through Miches, one would have to assume.

I wonder if there is another route passable by jeep, that passes south of the national park and connects to Bavaro via Miches? Does anybody know?

The Samana highway only shaved a bit off the Sto Dgo route, depending on where on the North Coast you started.