I'd like to see things that modify the mages themselves.
Perhaps mages could "level up" or "advance" in some way. Training cards could be introduced to the game that could slightly increase basic statistics like Life, Armor, Channeling, or Spell Points...perhaps skill cards could make you more skilled with using certain types of spells.
Exempli Gratia: (mind you, these are just "ideas,")
Life Increase: Physical training has yielded a healthier, stronger body. (+2 to starting Life Points)
Meditation: Time spent in deep meditaion has increased your connection to the unseen world. (+1 Channeling)
Grimoire scribing: Finding a cache of lore is always exciting. You have expanded your spellbook to include these new spells. (+5 Spell Points)
Dragonfire Secret: Learning how to channel Dragon fire makes your fire spells more potent. (Fire Spells do an additional die of damage for an extra 2 Mana.)
Lore of the Dead: You've spent some time studying the forbidden lore of Necromancy. (Summoning Undead creatures costs 1 less Mana.)
Conjuror's Aegis: Ambient mana from the rift a summoner's summons can be utilized to form a shield around the creature. You have unlocked its secret. (Summoned Creatures have an extra 3 Armor. On each turn, this extra Armor is reduced by a point.)
Stormrider's Lance: You have studied the arcane science of conductivity, and can call more powerful lightning. (Mage's Effect die for Electricity spells are modified by +1)
Voltaric Shield Runes: your wizard has embroidered enchanted Voltaric runes into his robe, enhancing mana flow and strengthening his Voltaric shield. (The wizard's Voltaric shield damage absorb is increased by +2.)
Voltaric Rune of Power: Your wizard's Voltaric runes include the Mana rune, which converts woven mana into energy that can be absorbed by the Wizard. (The wizard gains 2 Mana whenever a spell is cast directly upon him after its effects have been resolved) [requires: Voltaric Shield Runes]
Voltaric Rune of [Damage Type] Your wizard's Voltaric Runes include the [Damage Type] Rune, and acts as a shield against this damaging element. (The Wizard gains [Damage Element -2] while Voltaric Shield is "on." [requires Voltaric Shield Runes]
Nature's renewal: Your mage has studied the lore of Nature which governs growth and renewal. You can now infuse yourself with healing energy whenever you cast spells of Nature. (Whenever you cast a nature spell, you may pay an extra Mana to heal one Life point.)
Asyria's Second Scripture: Your priestess has devoted herself to the second scripture of the chant of Asyria, which governs spiritual wholeness, and has been enlightened by its wisdom. (The Priestess reduces the removal cost of her RESTORE ability by 1.)
Loremaster of Voltari: Your years of devoted study of all of the collected Lore of the plane of Voltari has yielded secrets to great power. (ARCANE spells cast by the mage have their Mana cost reduced by 1.)
Wizard's Schooling: You have returned to the grand college of Wizards, and have mastered a new school of magic. (The wizard may choose an additional training from one of the following schools: [Earth, Air, Fire, Water, Mind])
Beastmaster's Communion: You have wandered the wilds for months, studying the harmonious elements of creation. (The Beastmaster may choose an additional training from one of the following schools: [Earth, Air, Water, Holy])
Demonblood Elixir: You have discovered and performed a ritual most foul; to infuse your very lifeblood with that of a demon! (The Warlock gains the trait Flame -2)
Arraxian Demon-binder: You have made a study of long-forgotten black magic rites, and have learned many true names of demons. (Demon summoning costs in Mana are reduced by 1.)
Blood Magic: You have wrested the secrets of Arraxian blood-magic, and have turned it to your own ends. (Mage may substitute Life points to cast a spell.) [Dark Mage only]
Again, these are just ideas. I like the thought of leveling up and improving your mage, and giving him unique skills.