As a general rule, Spell Damage is more valuable than Max Magicka for doing damage; same is true for Weapon Damage & Max Stamina. Mostly this is because of the way most skills' effectiveness scales, and SD/WD can be augmented easier / from more sources than Max Resource, and also SD/WD is a stat that doesn't deplete or rely on recovery or anything like that (as in, you don't gradually "run out" of it during a fight).

Even if you could "even them out" in such a way that made them otherwise equal (which you generally can't), there's just plain more buffs that grow/multiply your Spell Damage (such as Major/Minor Sorcery, Major/Minor Courage, Powerful Assault's unique bonus, etc.) than there are ways to grow/multiply your Max Magicka. Again, same is true on the Stamina side of the fence.

As an example, if you really tried you could get your Max Magicka up to ~60K, but (aside from the small handful of skills that do scale better with MM than SD) you still wouldn't do as much damage as if you just got ~5K Spell Damage, since the two stats just aren't weighted equally. The vast majority of damage sources favor Spell/Weapon Damage over Max Resource.

The only other particular benefit of boosting up your Max Resource pool, aside from the lesser damage boost it does provide, is that having a huge pool of Max Resource to pull from kind of helps delay / ease the burden of sustain issues. You'll obviously be able to sustain fights longer when you have 60K Magicka in the tank than if you barely broke 30K, ya know? But even here, having a huge pool of Resource isn't often a great substitute for having adequate Recovery so it's still not a great option most of the time.