You can't view the races from the Casa Marina but it's a great place to stay for the quiet atmosphere. it's on the ocean and you will need taxi's or a car. Close to Louie's Back Yard restaurant......one of the best.
Parrot Key Resort is great but you will also need transportation to Old Town (Duval area)...........and the same for the Marriott at the entrance to KW.......used to be the Holiday Inn. It is huge condo style now and has a GREAT restaurant. Also VERY nice but not on the water and out by the airport is Grand Key Resort and some Hyatt condos
When I move from here..........when I come back to visit, I will want to stay at the Westin or the Pier House or Hyatt (for the locations).....take the shuttle boat over to Sunset Key for lunch or dinner (shuttle located at the Westin) and be able to walk Duval at night.
Most luxurious and $$$$..and you can see the races and cruise ships.........Sunset Key Cottages, off Mallory square
Now......anybody want to buy a house in Marathon...I'm ready to move to the real world.........

PD