I've found an awsome MP trick that with always leave you with a lot of MP. Link KOR or Master Summon with MP absorb (You get it in Wutai). It's that simple, KOR takes a lot of MP but with MP absorbyou'll regain a lot of MP 'cause it hits the enemys 13 times, same goes for master summon. It works really well against the Weapons and the last bosses!