My take on Rar/ex and materia:

Right now you can only put materia on non rar/ex equipment(everyone knows this, I know). The first attempt is 100% on those pieces of equipment. On the second materia attempt it drops down to 15% or more, depending on what level of materia you are trying to put on. So for the rar/ex gear for the first attempt on TIER I materia, make it a 20%(give or take a few) success rate. On the next attempt make it a 10%, third 5%, forth 2.5%. Something along the lines of that; Tier I materia!. For tiers above one. Make it next to impossible(improbable) to put a materia on the piece of Rar/ex gear. That's what I would like to see happen.