the whole idea of ship specifically designed as a test-bed for super-advanced technology and propulsion that could completely redefine Starfleet's core mission seems like cornucopia of story ideas.
Story ideas about endless techno-babble?
Whle I do think the show should be set on a starship, having the ship be anything more than a way to get from story to story likely wouldn't be that important. Kirk's ship was old, it was the characters and the situations that were the important part of the show.
A ship a mile long or one 500 feet long, not my first concideration. How many ober-powerful giga-phaser banks it has ... who cares.