Benefits for stats, given the current and most likely specs for 2.0, should satisfy a few things.

First, the gains from any change in attributes should be visible, either from a character sheet like World of Warcraft, or a noticeable difference in actual battle.
Secondly, due to the nature of the materia system, additional melds, 3+ for example, are extremely costly, and the gains from adding those additional materia should be reflective of that cost. Meaning that as you add more of an attribute, the gains at each additional attribute should increase.