I'm not a game designer, nor have I played AVWW enough to really comment intelligently on the design choices therein.
However, for theorycraft, there are some interesting possibilities.
You could take a WoW-style approach (say what you will about the game, it may be derivative and stale but damn do they have great spell mechanics): each spell (eventually, maybe just one or two initially, or maybe just the basic spell in each element) has a chance of proccing a special effect that cannot be taken advantage of with the spell itself. For example:
Basic fire spell: Every 4th cast causes your next non-fire spell to hit for 25% additional fire-based damage, and sets the enemy on fire.
Basic light spell: Every 10th cast causes your next non-light spell to bathe the target in light, causing it to deal 75% less damage for 5 seconds and lighting up the map for 10 seconds.
Basic earth spell: Every 5th cast causes your next non-earth spell to shake the ground, stunning all enemies within X distance from the target to be stunned for 2 seconds. This can only happen once every 30 seconds.
And so on.
Additionally, casting a spell repeatedly temporarily lowers your resistance to type of damage (representing your reliance on a particular form of power, reaching power-hungry status). It resets once you cast the opposite element, which also causes that spell to deal damage equal to double the amount of resistance lowered.
For example:
Casting a fire spell lowers your resistance to fire by 2% per cast, up to 20%. Your next (basic) cold spell will deal up to 40% more damage, resetting your resistance.
All of these could be represented visually with auras, which should definitely cut down on having to add additional artwork. I may have more ideas in the future. Conversely, if these ideas are dumb, feel free to disregard!