Xenoblade's Gem system is still my favorite "Materia" system.
You basically purify crystals and temper them to make the Gem you want. And if you're lucky and get the percentage past 300%, you get a perfect Gem of the next tier. And you can just add and remove the Gems whenever you want. You don't have to get a catalyst or be a certain level to apply it.
Now I wanna play it, if I wasn't in the middle of One Piece Unlimited Cruise.
EDIT: But on the subject of Materia changes. Hell yeah. I've only sampled a bit of trying double melds (got some STR gloves, that's about it). And I've seen some horrible stuff. One player I know has failed 40+ attempts on double-melding a Sarnga. That's just nightmarish.
