For a suggestion that I think can help the current system without a huge overhaul; materia needs to be able to be leveled up through the spirit bond system. The problem is that for the most part anything but tier 4 materia is pretty useless and attempt to spirit bond anything but over level 41 gear a waste of time.

They need to allow for a slotted materia to grow to the next tier after a significant amount of spirit bonding is accumulated on the piece of gear its bound to. Getting materia through each tier would take a good amount of time so those that wish to save time can still play the RNG game and get high tier materia instantly from high level conversion but this would also give another avenue for people to gain the materia they want without the need for tremendous luck or gil.