Once I can perform such a comparison, I can set quantities of spellpower which mark the border between first- and second-level spells, second- and third-level spells, and so on.
The reason I want to do so stems from the fact that some spells, as they are written now, provide a measure of scaling based on the caster's level. To take a well-known and classic example, the traditional Magic Missile spell produces 1 missile of 1d4+1 damage at 1st level, two missiles at 3rd level, three missiles at 5th level, another at 7th and finally another at 9th. Thus, Magic Missile remains a useful first-level spell even when the character has gained a lot of experience.
But why does this scaling of the effect this go as far as 9th level, and no further? That's the question I want to address: once I've quantified how much spellpower each additional missile is worth, then once the point threshold for a 1st level spell would be exceeded by adding an additional missile, the spell has reached its maximum capacity for scaling. To wit: suppose that my calculations determine that the cap for 1st level spells is 1000 spellpower, that the single-missile version of the spell costs 400 points all together, and that each additional missile costs 300 spellpower. Then, the spell would scale to 3rd level (one additional missile: 400 + 300 = 700) and to 5th level (two add'l missiles: 400 + 300 + 300 = 1000) but no further, as additional missiles would exceed the first-level cap.
In addition to the above usage, quantifying spellpower will also lay the grounds for player mages to construct their own spells, first by modifying existing ones, and then by creating wholly new spell recipes ... all at some cost, of course.
Obviously some experimentation will be needed to determine appropriate spellpower thresholds, and once that is done, there will naturally remain the large task of modifying spells which ought to be of a certain spell level so that they are reasonably close to their brethren.