I think that the gloves are different on Law and Paul, and perhaps Law's shoes? Except for Yoshimitsu most of the cast haven't had proper design changes and only suffer slight, minimal retouchs with each game (kinda like how Lee's unicorn emblem changes with every game, but not his clothes and everything else),
It's more notorious how the quality of the skin shading and proportions of the models are slightly improved from 6br. Tag "was" kinda of a compendium of things from 1 to 3 (including suits in some cases), It would be nice if tag2 could do the same, since most character were pretty much redesigned for 4, so there are true differences in the way (redesigns that were eventually "brought back" to how the locked before 4, as to shuu shuu bad advertisement).
BTW supposedly Harada (the producer for Tekken that has been at it since 3 I think) has supposedly disclosed some info about the game already and steadily does so in his twitter (which I don't have since I don't tweet). Supposedly he has already confirmed that everyone from 1 to 6 won't be in; the example that he gave was that Kunimitsu is not going to make it into the game.