You sir, get my star of approval!
But in all seriousness, the way I see it, tech has pretty much peaked in the SWU around this time, Tech can't get SIGNIFICANTLY better but it can be improved upon here and there. Add more armor there, or hey doing THIS makes THIS better etc. No matter what, you eventually are going to hit that point where, meh, we have everything so why bother. Even the Death Star wasn't "new" it just had more lasers, 64 I think, that were forced into one beam, same tech, different use.
As to why things have the same names, Star Destroyers, I present this scenario to you:
"Hey Bob, I just finished the designs on the new ship today, what should we call it?"
"Well, Star Destroyer is taken so why don't we call it.....the Aluminum Falcon Class?"
"Bob, shut the **** up."
You see, when you make something as big, powerful, and frankly ****** as an Imperial II Class Star Destroyer, how can you NOT call it something like Star Destroyer?
Aesthetics? Eh, who gives a ****.