I will explain:
Say there is energy ball spell, doing z damage. Researching advanced energy ball, allows for 1.2 * z damage plus an added bonus, say fire damage, or bonus against structures. (this bonus could be random)
Some examples:
Fireballs: More focused damage, stronger fire
Healing: Additional strength effect given, area heal, can heal non-flesh units, can un-heal enemy
Double strike: Triple strike, second strike is stronger or has an added effect
All Spells: Bigger range, faster recharge, added effects (e.g. fire), increased power of effects
Additional: Adept spells (e.g. adept fireballs) for a further increase in power, but only after advanced tech is learnt
--OR--
Normal -> Advanced -> Elite -> Adept -> Mastered
Turn cost for the techs would be about 6-8 for each spell.
Some spells will not have advanced versions e.g. lifelink
Could be researched in its own structure... e.g. magic tower
Hope you like