The phys/spec split is the best thing it happened to the battle system of pokemon in the last 3 generations of pokemon. Not only it put some logical sense into the moves, it doubled the amount of possible offensive set ups that a pokemon could have. Before if a pokemon had special type but it's moves were physical, he would be garbage, after there were suddenly two possible ways for that one type to work.
As far as advances (or additions) in the battle system it goes:
Phys/Spec split>Abilities>Hold items>everything else
