What warrants a suffix on a hull number?

[Kamen Rider Blade]

It just seems wasteful for the Federation given how environmentally conscious they are and the level of modularity on their ships.
Heck, they could easily REDESIGN an existing class of ship every 2 to 5 decades too (aka, part of a major refit cycle) and there you go, a brand new ship (despite the fact its the same ship from 50 or even 200 years ago is essentially brand new - the old one was just harvested for its raw materials so that new technology can keep getting integrated).

SF could still introduce new classess of ships as such over time if they wished - or older designs could/would be adapted to evolving mission parameters.
The existing Sovereign class for example might not look anything like it did originally after the first 50 years for example. And if we take into account that changes will only accelerate over time... then design changes would become more apparent after the first 50 years... but then even more would have changed 25 years after that... and so on... until basically every 3 to 7 years, 'standard maintenance' would effectively change the design iteration somewhat.

I'm all for brand new stuff, but if a starship like the Enterprise-E for example surives for the first 20 years... then why not just keep it in service... give it a major overhaul (pdate the design - if its needed) and continue using it?
After the first 50 years, the ship would have changed anyway.

Now, I can see SF eventually retiring certain classes of ships if they don't deem them necessary anymore (such as say classes specifically designed to do short range mission type stuff or planetary surveys - or just upgrade the class of ships so they can do a lot more - the Rhode Island was an upgraded Nova class vessel whose abilities included (in the original future from which admiral Janeway from 'Endgame' came) deep space tactical operations to boot and exploration.

Heck, 1500 ships of a given class could easily give SF more than enough to play with with design options until they reach about 2.8 million ships (which would be roughly 1.86 thousand distinct classes).

SF could limit itself to 5-10 classes of ships per century for example if necessary (but under extenuating circumstances, and if there's no other option, they could opt for making more if the times require it).

The main issue is large scale maintenance & training along with managing the logistics, that's really what holds things back.
The more parts in your inventory and the more things that need to be kept up with, the more complicated the training is.
There's a practical limit to how much diversity of StarShips & Shuttles you can practically maintain fleet wide.

IRL, Fighter Aircraft are simplifying down to one-size fits all.

Ergo the F-35 & F-22 paradigm. Regardless of how you may feel about those fighter craft IRL, the entire world is going that way for logistics reasons along with survivability.

F-35 is Primarily a Ground Attack Fighter as it's primary design trait with a Secondary (Second Best in the World) Air-to-Air Combat capability

F-22 is Primarily a Air-to-Air Superiority Fighter (Best in the World) as it's primary design trait with a Secondary Minor in (Air-to-Ground) Combat capability, obviously the F-22's (Air-to-Ground) capability pails in comparison to the F-35, but that's a side feature compared to it's main role.

Have you ever heard of the phrase "Less is More". Having less things to (worry about / fix / maintain), makes it easier to train more competent and higher quality maintainers.

Also less part #'s in your inventory to manage = Easier times for everybody.

Not everything can be replicated, some parts might need special facilities or the StarShip might not carry enough of the raw base material to replicate it without using exorbitant amounts of energy to manufacture it.

Remember Replicators don't turn raw energy into matter generally, that's TOO energy intensive, it converts existing matter into what you need, that's far cheaper on a energy cost scale.

Just look at replicating Small Shuttles in Prodigy, just replicating one shuttle ate up a giant % of the energy output.

There's a reason why resource management is critical, it's not to willy nilly burn energy in inefficient ways if you don't have to. Especially using resource intensive ways like raw material replication from base energy. It's always far more energy efficient to replicate using base matter that is close to your output and adjust as necessary, that's far cheaper (energy-usage) wise.

Remember, during the Dominion War, Nog had to barter with other StarFleet Ships/Facilities to get certain parts.
Not every part can be replicated locally, so the high precision and quality of certain parts might not be easily obtained via Replicator.