Spells should have boosts, as units do.
Faster Cooldowns, Wider Ranges, Longer Durations, those are just the obvious boosts to start with that could be applied to any of the spells really
But for more interesting game play it would be cool to see something like, anytime Firestorm is used, the “fire” don’t just radiate the Hero, but Pyromancers too or something.
Along with the Doom Gate & a unit boost, a spell boost would be cool to earn in wars instead of two units.
Just a surface scratch of an idea…