I'd suggest some "spells" or "skills" as benefits to ranking up. Maybe add tile bonuses in conjunction with spells. Like, change a front row tile to forest and my wood unit gains +attack/+defense or some other special unit skill bonus to terrain. Makes for more interesting tactics. Also, "wound" seems too generic maybe some other status debuffs.
It'd be nice to see each skill tree come with inherent bonuses/attributes. Ice already has freeze/slow, show about stun with divine and burn dmg with fire?
 "Highgrounds"){kind=icon}
 "The Peacekeeper"){kind=icon}
 "Learn to Fly 2"){kind=icon}
 "Wizard's Run"){kind=icon}