Just like with Penury, the Max you can achieve with this is 50% cut in Mp cost.
Not true, Conserve MP can activate on a spell you use Penury on. I've seen Curaga II fire for 30 MP before.
The stuff about cure cast time & fast cast combined being able to exceed 50% is rather interesting, though. Good catch, Rya. I'm curious to see what comes of this.