I was fiddling around with intelligence and how it affects AoE size, and I came up with some suggestions that would make them generally better.
1 - Spell casting range
All spells - AoE included - have a casting range, but that range is never displayed in the game world when casting. It would be beneficial to have a visual indicator if you can cast a spell from where you currently are, or of where you will have to move to cast a spell on a location.
2 - Adjustable AoE
One of the benefits of intelligence is increased area of effect. It turns out that this can be a rather big problem at higher levels. Here's an image:
This is a 20 Int wizard casting Dazzling Lights. The wizard is at his maximum casting range for the spell, which just so happens to be in the area of effect of the spell. Casting this spell will cause the wizard to dazzle himself. Needless to say, this is rather undesirable.
On top of this, the huge AoE of some spells at high intelligence will tend to make them difficult to use in constrained spaces without, say, torching your buddies.
As long as friendly fire is enabled (and it should stay enabled, personally), the player needs a way to have high intelligence without it ending up being detrimental. Making the AoE spells have a reducible range would help quite a bit. If this would unbalance spells from a tactical standpoint, then it might be enough to allow the player to cast spells at an effectively reduced intelligence (i,e., keep AoE and duration coupled).