Imagining an Ambassador era California would probably involve nacelles with the characteristic topside opening (although perhaps pointing down or to the sides), in addition to the blue lateral/wraparaound "field windows"; a bit fewer portholes on the saucer (the Excelsior kitbashes of DS9 liberally added TNG style portholes when deemed fit), aaaand... What else? Shorter strip phasers? Perhaps even turret phasers for the extra granddaddy flair? A blue "enclosed" deflector such as in the Connie refit, the Excelsior and the Ambassador, although perhaps a bit more oval? An angled saucer rim?
You can easily do "old" with a circular saucer and a midsize starship, so TPTB here chose well...
I'm sorta looking forward to the episode where we finally see a "known" starship in glorious animation, and can compare it to these all-new creations for determining how "accurate" or "serious" we're supposed to find the depictions.
Timo Saloniemi