In WoW Classic, Intellect mainly increases your mana pool and your chance to critically hit with spells. It does not increase spell power or healing power in Classic.

What it does

  • Increases total mana.
  • Improves spell crit chance.
  • Helps casters stay active longer before drinking or running out of mana.

What it does not do

  • It does not directly raise spell damage or healing in Classic.
  • That means a piece with Intellect is not the same as a piece with spell power.

Practical takeaway

  • Mana-heavy classes like priests, mages, warlocks, and paladins usually value Intellect because it supports longer casting and extra crits.
  • For damage output, spell power is the stat that actually boosts your spells in Classic.

TL;DR: Intellect = more mana + more spell crit, but not more raw spell damage/healing in WoW Classic.