I am sorry that I did not reply your post this before your ride. I used to go that way as a commuting route and also a ride before and after work. Makes a nice quiet way to the sound.
That little path saves you from that nasty hill climb on Rte 1 (Fort Hill) that has a narrow shoulder and busy traffic. It and also adds some scenery to the ride. After the pavement ends it is pretty rideable until a sand patch before the old trolley bridge . There used to be a no trespassing sign on the gate to the road along Mumford Cove. Both this section of Groton and the next community along the sound (Groton Long point) are those little seaside enclaves, and even though the roads are public, one gets the sense they want to keep outsiders out, so I doubt a path will go any farther.
I am reading the original post here are a few east/west routes between New London and RI- Rte 184 comes to mind. But these are further north and add distance and unfortunately hills. Rte 184 to Mystic and then along Rte 1 to Stonington and then there are alternates to that nasty section of Rte 1. The coastline east of Westerly is nicer than CT's coastline I think,
This a route that I would suggest. Misses most of the bad spots and is scenic.
http://www.gmap-pedometer.com/?r=6025958