A ship might have a 50 year old hull barely capable of sub light speeds. You just try strapping that brand new warp/wormhole drive into it and see how long it takes before you turn the crew inside out...
the ENGINES are barely capable of sublite.
the hull is just a box or frame to hang systems off of.
assuming the hull has enough space for warp drive, AND the protected crew area that requires, no biggie.
About the only thing you need to worry about with hulls is fatigue wear and mass to space ratio. Armor is best modeled as a separate system from the hull.
Well, if we go with "realism", at some point a hull will become obsolete. Lets say the newer Modules have Ferro-fluid-bullshittium-wireless-energy sockets for enery transfer, yet these energy cables need a special form of shielding that would mean the whole hull needs to be besically ripped apart and rebuilt so the cables could be integrated.
Or newer ships hulls are made from newer materials that make them lighter, more endurable, whatever.... is there much point in producing the old hulls with the newer materials? Isn't that already a new hull?
I see that mixing "current day realism", which means taking ships, tanks and other vehicles as reference, with "sci-fi / future realism", which means space ships, and technologies barely understood even in theory today, is making this thing much more complicated.
Yes, there will most probably be little reason to change hull shapes in space, where there is little friction. Maybe even the savings in weight is not that important when a slower acceleration just means spending more time and fuel to get to the same end speed (altough fuel consumption WILL be a problem, save for some advanced future tech that makes fuel obsolete for space ships). There will still be plenty of reasons to move away from a very old hull.
And then, there is player expectations. No matter how much we think we know our science and are ready to ditch cheesy exploding cars for more realistic outcomes of a car being damaged, at some point most people are dissapointed by "realistic lasers" in movies for example. The horribly unrealistic, 50's cliche Star Wars laser cannons might be giving any physicist headaches, but they do look and sound much cooler to the average person, even though they do not make sense.
So having hull types become obsolete as they age is something people would expect, because that is what happens in our world. There might be exceptions (like the M2 12mm Heavy Machine gun still being the state of the art western heavy machine gun after almost 100 years of service life), but generally, most vehicles are in dire need of upgrades after a mere 10 years, and most become oboslete after 20+ years... some are obsolete the day they are built because of some rapid shift in technological advancement or strategies.