Cheebs, thus far the Star Trek franchise has been concerned with establishing a strong sense of continuity. They also do time travel a lot in all the Trek series, but when they do, they improve the quality of the animation / models without altering the designs. Revisiting the same time frame with different actors is a neccessity because actors die. "Recasting" the ship is a bit different.
Canon and all that. The natural evolution and improvement of Federation design mirroring the ability of real producers and special effects folks to realize better looking ships, which is why we have an Enterprise NCC 1701, 1701-A, 1701-B... That's the way it's been, and it works out fairly naturally.
I'll see the movie and hope it's better than the source material, because I have no regard for the source material. The ship itself getting a massive facelift and looking different upsets some people that do. I don't care much because I never cared for Kirk and Spock et. al, but I can sympathize.
Don't get me wrong, I get how this is an attempt to do something different because what they were doing wasn't working. But thus far, the franchise hasn't been operating on the same paradigm as Bond or comic books or whatever, so you should be able to understand that longterm fans won't necessarily appreciate the paradigm shift.