I suspect that, like technology today, miniaturization of existing tech into next-gen platforms would continue to make things smaller over time, even into the Trek-era.
To a point yes.
Although I like to point that at some point they stop really caring about it. I like to use the example of Picard's "laptop" thing. "Ugh, see it's already so outdated look how big it is." So? At that point, it's a design/aesthetic choice. We're obsessed with making everything as small and thin as possible today... but there's no particular reason that will persist 300 years into the future.
The general idea that "bigger = better" is odd though because alot of times, something being bigger does imply that it's LESS advanced, due to miniaturization. Like, why have a massive ship will 47,000 crew on board when you don't need them?
Size should only really play a factor in mission/role. Something like the Galaxy-Class was intended to be a super long range exploration vessel, so it needed... space. Realistically, most of the E-D is probably just empty space. If the crew was evenly dispersed throughout the ship, utilizing it's entire internal volume, you could likely walk around for a day and not run into anyone. Most ships don't need that. Hell the E-D didn't need that because it didn't go on long-range exploration missions.
It's why I also don't mind the USS Kelvin being hella huge, although should be a Prime Timeline ship. I figured it was a colony support vessel or some such, so it's a gigantic ship filled with cargo, shuttles, etc.
All fair points, but the Galaxys are treated as top of the line in some measure, and when we look at a possible future starship with the J it's shown to be massive.
We don't know what the intended mission of the Universe-Class (going with STO nomenclature) is. The ship may be designed for extra-galactic voyages and essentially never return home.
