At the end of the game, MP becomes REALLY important to maintain. Mostly because CURE is the only thing keeping your HP up. However, restoring MP is tricky because Ethers really don't restore all that much, and besides Elixirs, that's all you've got. Elixirs are important because you have so little inventory space that Ethers just aren't an option. You'd waste all your space just giving yourself enough to restore one person's MP once. Not to mention that you need to carry other things like Pheonix Downs.