Actually, I found the coda appropriate. Throughout the movie, the characters were all carefree and joyous, but they were going nowhere fast and they all sort of recognized this. Richard Dreyfuss and Ron Howard's characters actually were going to leave their home to be somewhere.

So when the four of them actually make their decision on where they're going (in an attempt to keep this from being spoiled, I won't say who leaves), the coda shows that while the ones who stayed remained in a dead end they set for themselves, the ones who left actually lived a fulfilling life and probably saw the world with it.

That's just me, though.