I remember feeling intrigued by the idea of a ship called El Dorado, i.e. naming a starship after a fictional place. Then we got an actual space shuttle named Atlantis!
So how about Nebula-class USS Shangri-La?
I'm not sure if you're aware of it because it wasn't mentioned in the post, but USS Shangri-La
CV-38 was a US aircraft carrier for almost 30 years. The name commemorated the Halsey-Doolittle Raid of 1942.
USS Eldorado, Fleetwood-Class NCC-1959.
I always thought of Pacer, Gremlin and Matador classes when I heard "Ambassador class."