After reading all of the arguments on this thread, I think that I have changed my mind about wanting Dual Spec. I actually agree with many of the points made here that picking and sticking with a spec was part of the identity immersion of the game.
But I still want those classes to be viable enough that people can play them. I still think that was a really bad part of the original vanilla, as I had a LOT of friends in my guild who started out in one area of a class, and tried to take that area of the class into end game only to find that they couldn't and were "letting down their friends". So I still think that alt specs and/or gear needs to have some minor numbers and things looked at.