Magic Charge-Casting System

I would like to suggest an overhaul of sorts to how stave spells work, both in damage and cost. Imagine: the longer you charge a spell, the more mana it uses but also the more damage it does. For example:

Quick Cast (tap) .5sec cast, 15mana, ~80 damage. It's fast, cheap, and something you can cast even when you're very low on mana. Great for finishing low mobs. Similar to wands but requires mana.
Medium Charge (hold ~1.5sec) ~1.5sec cast, 45 mana, ~300 damage. Small AoE, close to current Eternal Fireball behavior and damage.
Full Charge (Hold ~3sec) ~3sec cast, 120 mana, ~800 damage. Tactical nuke with a large AoE. Big risk standing still for 3 seconds for big payoff.
Damages would also be modified by your intelligence score, same as magic damage is currently. So, a lvl 5 character doing a full charge will have a fraction of the damage that a lvl 45 character would.

Another option is to tie damage totally to mana usage. I.E. 10 mana per .5s hold leads to damage equal to mana * intelligence score. (Note, this is similar to how heal channel already works as well.)

This system would synergize really well with multiplayer and the other classes. Your melee players would buy the glass cannon time to light off the big gun and possibly turn the tide of battle.

Charges could be interruptible as well, resulting in the spell doing half the damage of the next level up.

As things stand currently in game, mage is a very resource heavy playstyle with not much of a payoff until near endgame. A system like this would add depth to the mage classes as well making them feel less useless in the early - mid game.

This charge system also would lend itself wonderfully to the alluded to upcoming utility spells. Image an ensnare spell that roots longer the more you charge it, or a speed buff where charge time dictates how long the buff lasts. This could turn the mage classes into a real tactical role in group play beyond ranged DPS with expensive use costs.