Mythologically, of course older is better than newer.
There are lots of emotional reasons. . . .They don't make them like that any more. . . .The company started going to heck when they changed/deleted/added ???????. . . .Etc.
I think it is worth noting that "emotion" is pretty much why we have these guns at all isn't it?
The only two guns I actually "use" is a J-Frame for concealed carry, and I upgraded my outdoor carry from a revolver to an HK running .45 Super.
It's not that I couldn't hike with my nice S&Ws, but I don't. They see range time, but are nothing other than pleasurable luxuries at this point.
As such, why not have the guns you find you have the largest emotional connection to? If a gun doesn't "Spark Joy" (as my wife's TV show lady says), it goes on the chopping block to make way for a gun that does. BUT. The key there is the second line. Sometimes I wish I had some guns that are gone, but then I look at the guns that they made way for and that feeling evaporates.
In this case, if I am going to weigh in on thinning the herd: Only part with the 4" if it's for the express purpose of acquiring a gun you like more. If the S pleases you, don't part with it unless its in pursuit of a 4" S.
Or unless you are gearing up for the big jump to something like a 3.5" or 5" Model 27, or a Registered Magnum.
Much of the reason that buyers think that old is better than new is because the old ones do not have problems. Well there was no Internet in 1957 we passed the stories around the water cooler, over a coffee or a beer. 10 million people did not get to hear one customer yelling that he was wronged. Of course the old ones had problems. The things that were wrong with that 1950s revolver had been fixed by the Factory years before many of us were born. So we see them as trouble free.
This is an excellent point that feeds into the current mythology around the S Range guns.
The service department was excellent, and a gun repaired by them may very well be extra nice. My experience with their work (honestly the main thing I look for in old Smiths now), has been phenomenal.