The trainable spell system for Mages and Wizards has gone through a number of upgrades and fixes as follows:
(1) there was an error in the way that spell damage was calculated for training a spell higher. The more you trained, the less of a bonus you got.
(2) base spell damage has been drastically increased for all spells by about 60-100% more damage per spell.
(3) in addition to spell damage bonuses being fixed (for training spells higher), spell damage bonuses have been increased significantly (from 5-15% to 25-150%).
(4) mana cost has been reduced slightly for spells trained to level 2.
(5) preparation time reduction has been lowered for higher-level training.
Please let me know if you experience any problems with the above changes, though they should all be in your favor.