I don't disagree with any of that, except that it seems like an old vise is sort of like an old gun. It is more likely that an old Parker gun is going to have some problems, but it's hard to find a new gun that was made to the same level of craftsmanship. The Wilton vises still made in the USA are probably the closest to it. After all, your vise is nearly 30 years old now.
As for big vs small, I also agree that the big bench vise is more versatile and should be the center point of the work bench. But there is also a reason that engravers, checkerers, etc have specialized vises. The analogy probably should have been a crew cab f250 vs a sports car /mini van/ sedan / Jeep / 4 wheeler etc. There are not many things that an f250 can't do, although for some tasks a specialized car might do better.
I'm almost finished with my Parker restoration, and I'm going to get my Wilton 6.4" Tradesman restored next. It's not to the standard of a 500, 600, etc but I doubt I'll be able to tell the difference. After a decade or so of service at Seacor Marine, it's still pretty dang smooth.
What do you mean by a keyed bar?
Also, a 4" craftsman is what I'm replacing... No need to convince me that they are different animals.
