What about greater spells that require 2 or 3 maxed out spheres of magic to be able to cast. Some suggestions (spell names are added for flavor =):
1. Apocalypse: Fire 3, Death 3, and Entropy 3, kills mage or lich on use, uses atomic bomb animations, and kills all units in a tile, all buildings including wonders and halves population in city. All known good and neutral civs declare war on you. Bumps Armageddon 25 points.
2. Death Wind: Wind 3 and Death 3, Uses radiation animations. Acts as fallout.
3. Blizzard: Wind 3 and Water 3, Same effect as Blizzards in BTS scenario
4. Magma Fields: Earth 3 and Fire 3, Unrepairable Broken Land effect.
5. Mana Mend: spell type level 3 that you want and existing mana type level 3. This spell will allow you to change a mana node to a new type.
6. Treasure Trove: Earth 3 and Chaos 3 - removes/distroys gold, and gems resource tiles and grants the player 3000 gold.
7. Glory Divine: Spirit 3, Life 3, and Body 3 - removes disease, heals, heals plague, blesses units.
8. Righteous Anger: Body 3 and Spirit 3 - plus 2 strenght negative 4 defence.
etc...