Hm... that would make it a no-brainer, and I'm afraid that would make it boring. However, I agree that it would skyrocket the Wizard into a sphere of near-unbeatability (man, isn't that guy flexible/powerful enough already?). The third spell option is extremely valuable because it allows you more flexibility in the two actions which are most powerful/flexible anyway: your Mage's actions. I cannot think of any Mage who would not want this for 5 mana and 1-3 spellbook points.
Long story short: I hope this card will never enter official play - an essential part of Mage Wars, in my opinion, is the challenge that you can only prepare two spells; admittedly, there are some tools which help you (wands, spawnpoints), but they appear way more limited (position, cost, application) to me than this tome.