Don't skip Nantucket! It's really beautiful and the Boat Basin is great.
Rather than Groton, you might consider either Mystic or Stonington. Maystic, of course, has Mystic Seaport. I don't know if you have to be a member to tie up to their docks overnight but if you do, it's worth it. After they close the gates, you and the few other boats on their docks have the grounds all to yourself. It's magical. And in Noank, which you pass on your way up the Mystic River to the Seaport is Abbott's Lobster in the Rough restaurant - it alone might be worth the trip. Dodson's marina in Stonington is an excellent facility and the town, Borough actually, of Stonington is charming - lots of antique houses, antique stores and nice restaurants. Another cute and quaint Connecticut town is Essex. The Essex Island Marina is another great place to stay. [All of these places have websites.]
There is an article on Point Judith in the most recent Northeast Boater magazine. It didn't make me want to stop there.
All the best,