Should I be upgrading my skills? The added damage or bonus is great, but they use up so much more mana. When you reach the higher levels does the mana cost start to go down?

the mana cost goes up because the damage goes up....therefore you use less spells and deal more damage makes sense? i think so. higher lvl spells = higher mana cost. higher lvl = higher mana pool.

No, but when you reach higher levels, your mana pool goes up.

Upgrade the ones you're using a lot first, as they do get more and more helpful as they grow stronger.

That's right

Alright, thanks guys.

For any future readers:
The question with spell upgrades isnt mana or lack there of, it's lack of gold, upgrade only spells you use - there's no point of upgrading BSoL on a fighter or MMM on a mage.

Also, as said above, your mana pool goes up as you level - it also goes up if you put points to intel, but that's not very useful for a fighter.