No, but it's one of those things that adds up. If you look at some of Nintendo's other major properties -- Mario, Zelda, Metroid, etc. -- they've tended to see quite a bit of visual differentiation between entries, in a way that keeps the games visually related but still stamps out a unique identity for each entry. With Animal Crossing you look at screens from literally any entry in the series and they all look superficially the same, to the point where you'd need to actively dig around in bullet-point feature lists to tell what the differences are between the game. Even the Harvest Moon games have started designing new townsfolk, switching around visual styles and motifs, and branching off into variants (like Rune Factory) at this point.
I mean, it's entirely possible that AC will be a huge hit and "the exact same game, but with a decent number of real feature improvements" will actually have been the right thing to put out. But if it isn't, I don't think suggesting "hey, maybe this game shouldn't cultivate the image of being exactly the same game repackaged over and over" would be crazy.
That's fair. I don't think they should change it too much, but just enough that you can tell at a quick glance that it's a new AC game. I don't mean that only huge gaming/AC nerds should tell right away (because in that case, the current look for the 3DS game is enough for us to tell), but most players.
On that subject, I sure hope the new Super Mario Bros. game for Wii U will look different from the current version. Apart from the Miis and higher resolution it looks exactly the same as NSMB Wii. That game created confusion by having some people think it was just a port of the DS game, and that had updated visuals and an all new 4-player mode. This time people will be either confused by the fact that it doesn't look different from the previous game, right down to the title (only 1 single letter changed). People who know better like us risk dismissing the game as lazy.