There were priest units?

That is a great idea, because it would make units more interesting.

Not yet, but hopefully soon.

I think unlockable traits that add specific spells is the best way to go.  Don't tie the spells items.  Keep the staves as the ranged attack and have traits that allow you to customize your units with the set of spells you think best. 

Yup, I agree that spells would be better on traits than items, but it may be that the engine can't do it that way.  So far, the traits all seem to affect only stats, not combat abilities (ie, there's no stats that give a new ability to a unit, just affect the existing abilities).  May be a limitation of the engine.

I think the point of being able to create "magi" units was as a counter to archers if you decided to ignore the Warfare path.  Unfortunately there's currently no benefit to focus on a given path so most tech usually level up fairly evenly.

I added some items for specializing in healing to the community content thread. Please add any ideas you have about items, spells, and traits there. 

I agree that mage units need some love, I see them being very fun and potentially very powerful. However at this point if we decided to start allowing them to drop aoes at higher levels and wear armor (seeing as how there is no penalty to wearing armor and spells, thus why used robed mages?) they would be a very uber army clearing unit.

This.

And only stave units can have access to these Spell Traits.

Most of the hero special abilities, like Crushing Blow, are trait driven.  

Sweep is a Trait. True Strike is a trait. I think Maul is a possible trait for monsters (unless bears use a faux weapon for this).

I agree that there should probably be Life Priests and Death priests ... but please don't give them berserk: what a useless spell

I think something much better would be Blood Rage: +50% attack, +2 initiative, lose 5% health per round.