I wish that Starfleet as shown on screen represented a greater diversity of ship design, with ships of obvious Vulcan, Andorian, etc, build. I understand (and approve) that they would still need a common livery and registration system to represent a unified "face" to other polities, but the extent to which design is shared seems.... wrong. "Oh, we *greatly* value IDIC... now make sure your ships have saucers and use these warp nacelles made in Iowa."
Design diversity might have had value in different circumstances we've seen the Federation face. Even just a throwaway/background line about how the U.S.S. (random name) had a Vulcan designed ring drive which was unaffected by the Whale Probe and was standing by for evacuation would have been nice in this regard (as well as a good opportunity for the Federation President or Sarek to deliver an "I'm not abandoning Earth" sort of line).
Theres more benefit to shared design. Training, interoperability, maintenance, replacement parts, resupply and the design process itself are all easier when you have a common design. The main source of diversity should be ergonomic and environmental.
A species with the average height of Yoda might want ergonomic modifications that improve use-ability for their species, from desk, chair, access panel heights to console layout. The same for a very tall species.
And of course, Andorians might prefer the atmospheric controls set to temperatures that humans or other species might find too low for comfort. Vulcans might like it a bit too warm for some. Other species may prefer gravity that is 20% stronger or weaker, etc.