Spread life and death.
Henzell says...
  1. Gives you an extra spell slot for every half of a level in spellcasting. Raising your spellcasting also gives you more MP, and slightly boosts {spell success} and {spell power} for all spells.
  2. If your sole concern is one spell's success and power, train Spellcasting if it's 1/4 the cost of the school of a single-school spell, 1/2 the cost of the cheapest school of a dual school spell, 3/4 for a triple-school. If you want more spell levels, more MP, or have multiple spells from different schools, Spellcasting is more attractive.

Information based on master branch and the great LearnDB.
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