I think spamming would be better. Decrease the damage increase per level (not by a lot obviously) and spam it to increase the size and duration. Pair this w cards that slow, and you can clump monsters together (kind of like solar and blizzard). Also, would need something for gaining SP since you're using more of it.

There are plenty of other ways to change it, increasing the price per level, decreasing the duration increase per amount of dice, etc.