There's an Italian restaurant on River Road in Westport (name escapes me) that's just past the I-95 bridge; the deck overlooking the water should have a perfect view of Saugatuck River bridge. Also, Mario's, across the tracks from the station, is a great old-school bar. Good red-sauce Italian.
The Captain Daniel Packer Inn in Mystic, Conn. has a view of Amtrak's Mystic River bridge-- downstairs bar is great on a fall/winter day.
As I recall, you can also see the Corridor from the deck of the Skipper's Dock in Stonington Borough, where it crosses the head of the harbor on a causeway (this is where The Bostonian got trapped in the 1938 hurricane: they loaded the passengers into the baggage car, cab and tender and cut the rest of the train loose, plowed into Stonington through five feet of salt water. Wild story.)
Up the Danbury Branch, there's a restaurant called the Station House in West Redding, CT, with a front porch that overlooks the tracks. Many years ago, the porch was actually connected to the platform.