About the only game I've played that's managed to make horizontal progression somewhat fun is Monster Hunter, and that's because all the enhancements are upgrades to your own play style rather than changing an integral part of what you're using. Materia based horizontal progression once again, however, leads into the problem of illusion of choice, as there will still be one clear winner when it comes to DPS, to the point that they might as well get rid of the option and make it a baked in part of the job. More interesting stats would be great, but having something that changes the very core of a class just sounds like a whole lot of bad decisions waiting to happen.