I know I certainly wouldn't be sad. If I was so distraught over how my character's face looked, I'd happily pay for a cosmetic change in a heartbeat. Seriously.
People have been clamoring for updated player models ever since the Burning Crusade, and even MORE so when Wrath of the Lich King came out. I mean.... Having a Vrykul standing next to a Human or Orc, the difference between the detail and structure was enormous!
It has been about four and a half years since the first new races (Draenei and Blood Elves) were added to WoW – and even they are starting to look kind of dated in comparison to Worgen, Goblins, and especially Pandaren.
On a more technical level, the way the Pandaren monks moved? Beautiful. Just beautiful. But I can't see -any- of the vanilla races having the same flowing movement to them with their rigging. It's going to look stiff and awkward...
Now, I don't know about the rest of you, but I would happily have a major patch come out with no new raids or dungeons or whatever. Just have it be a massive model update. As others have said, it is strange to have three, soon to be four, expansions worth of graphical changes layered on the original one.
Take that tiger that was shown in the Art Panel, for instance. It's stunning! Now put it side by side to an old-world tiger you'd normally find in Stranglethorn. There's no comparison.
Now imagine that blocky tiger next to your shiny new Pandaren.
While I know a worldwide remodeling is obviously a MASSIVE, if not currently impossible, undertaking given the time restraints, it is a dream of mine since WoW has no sign of slowing down for years to come. How it is going to look when we have seven expansions out and we're still using the original WoW models?
Now, I could certainly live with NPCs not being updated right away, but I really want to see new player models for the original races and maybe some touch ups on the Worgen. The males look pretty good, but the females.... D:
In closing, I'm saying this because I am super thrilled with Pandaria and the gorgeous artwork and landscapes (and Pandas and monks). The amount of hard work the art team, animators, and everyone had to go through to make that possible is astounding. Though with all that said, it's going to look mighty strange to have my old-world Human lingering around in the middle of it.