Hrm...Ok, so far, here's what I have in mind for spells. All spells have a maximum application and a minimum application.
Basically, how much they can do to how much they will do. For example, Fire Bolt is 2
quanta, and has a minimum application of 3 damage to target.
The maximum is technically unlimited, but let's say 520 damage to target, since that's the current maximum HP anyone can have (barring the spell-reflecting shields, there is no reason to not hit your opponent with an attack that is that powerful) Or to use a trickier example, Thunderstorm is 2
quanta, and does 1 damage to all enemy creatures. Minimum application is 1 damage to 0 target(s), while the maximum would be hitting X(being the max number of creatures you can have out.)
For buff/debuff spells, I'm going to springboard off of your earlier discussion of Power/Resilliance. Blessing, for example, gives a creature +3+3, increasing both it's power, and resilliance. Liquid shadow, gives the creature the vampirism ability, which can increase the TTW of your opponent, while placing a flat limit on it's resilliance (That one's a metagamer).
If we judge spells as thus, we should be able to get a good idea of the base value of a spell, without having to consider the cards they are used on.(Using deflageration on a bone shield to using it on a Gravity shield)