Neglecting this Magic could force you to grind even more than you already need to.
I've made a few mistakes in my first playthrough of Quest 64 in nearly 25 years. This resulted in the second boss (Zelse) annihilating Brian.
Since Fire has the worst build, I was avoiding it completely, but I completely forgot that I needed to level it up to 7 to unlock Power Staff, which increases the power of your Staff Attack.
I could have already unlocked Power Staff if I hadn't put too many Spirits in Water, Wind, and Earth Magic.
Another mistake that I made was avoiding two-thirds of the enemies from the ship in West Carmagh to Normoon, because I assumed the next boss had only 400 HP (double of the previous boss).
Zelse has 680 HP, so he can be easily beaten with just the Staff if you have access to Power Staff and a high enough Defense.
I've only increased my Fire Magic by three Spirits walking back and forth in Cull Hazard twice. This is also a great location to grind for HP, MP, Defense, and Agility. You need to battle Blood Jell's at close range and hit them with your Staff to increase your HP. When they hit you with Homing Arrow's it will increase your Defense, and when it misses, it will increase your Agility. After each battle, use Healing or Healing 2 to increase your MP.