Yeah, in ICRPG, there’s almost nothing that happens automatically without making a roll using the appropriate stat to meet or beat a target number.
In our games, a mage could cast a spell without making a roll, but he or she would have to “burn” it, meaning they couldn’t cast it again until after a full rest in safety, which almost never happened in our games. A variant of this rule would be that the mage might have to burn it permanently to get a free effect or push the limits of what was possible.
I also think spellburn, a strict mana pool, or even outright spending hit points are great limiters. Another one might be limiting a spell to only once per encounter or scene or location.
That being said, I never want characters to feel like they aren’t awesome. So, unless the character is just simply hogging the spotlight, to the detriment of other players, I’d also just let the person rock on being awesome. But they still have to roll to cast. In that way, the target is always the great limiter or equalizer.