Onscreen, though, individual ships seem to rarely last more than 20 to 25 years. Sure, there are exceptions of older ships sticking around, but it seems more common a practice for Starfleet to introduce a bunch of new designs every decade or so.
Windows are better for personally experiencing things. With your actual eyes instead of a digital image.
Think about how useful a window would have been during Wrath of Khan. Yes, in reality, seeing anything at the distances stated in Trek would be virtually impossible.... but this is Star Trek! Since when have they cared about reality? Shaw even had crewmen acting as lookouts using the windows to watch for the Shrike. So windows are clearly useful.
Exactly. People pooh-pooh windows as if it's some archaic technology. In reality it can be quite useful, and doubly so in Trek reality.
OK, so in my head-canon, the new bridge windows now have some form of ablative armor that pops out over the area instead of sliding in place like a sash.
Introducing new designs and retiring old ones are not necessarily the same thing though. Fine with Starfleet coming out with new designs and expanding the fleet – less fine with them going all Logan's Run on established ships that have proven themselves the moment they reach double digits.
I draw the line at Picard sending Geordi to look out of an Enterprise window at things because his VISOR is apparently better than the entire sensor suite of a Galaxy-class ship though...
Yeah, that was odd. I think early on the production wanted to reinforce Geordi’s VISOR was superior to regular eyesight (for folks who had maybe missed the premiere) and that was just one way they could demonstrate it.
In my head canon the Dominion War had a huge effect on ship longevity. The ships that survived, especially prewar builds could potentially have suffered multiple large damage events. Repaired and fit for service but retired once decent replacements were available. You also tend to have large technological advances during war time that some frames possibility couldn’t handle. So while the Galaxy or Intrepid may have been present in Nemesis they might have been “good enough” while the fleet was rebuilding. There was also a large loss of trained personnel and you probably had a lot leave service after the war ended. Reallocating personnel to new builds makes sense.
Yeah, they key point is that 100 year service life for the Enterprise-D included regular refits and upgrades. Without those upgrades it might still work and do its job, but it'll be hopelessly outmatched by rival starships. There probably comes a point where it's no longer worth upgrading an existing ship to keep it running, and it either gets mothballed or scrapped. Possibly with advances in replication etc, it's now easier to build a new ship and reuse/recycle components from an old one than it is to keep the old one up to date. That seems to have been the case with the Titans, and possibly the Enterprise-E.