Alternate Wizard Spell Rules.

[papastebu]

One problem with granting spells at lower levels is that some spell effects are dependent on caster level, and others are not. I like the idea, but it'll take a lot of thought to make it balanced. A 1st-level fireball may do only 1d6, but a 1st-level Power Word Kill will take out even the typical 10th level character. You'd have to make spells like that scale with caster level too, I think, for it to be balanced. Maybe have it kill someone whose current hit points are no more than caster level x5, though that makes it slightly less powerful at high levels. Just a thought.

I have done with this project what I do with most others: gotten off to a roaring start, but run out of steam after a bit. The reason for the use of fireball as my example is that it has a scaled damage, range, and area. I was trying to show how I would break down the increments of such spells. Effect spells are more difficult, but they can be scaled also, as with prismatic spray in the example above.
But let's break Power Word: Kill down a bit.

Currently, it instantaneously kills any creature with 100 or fewer hit points and no magic resistance.
Scaling this down shouldn't be too difficult. Since it is currently--in my system, there is conceptually no cap on how powerful a spell can get, but it can take awhile to get some spells up high enough to do as much as you want--a ninth-level spell, we could say any creature with 10 or fewer hit points or one hit-die per spell-level would be affected, creatures with more hit points than the per-level allowance, or higher hit-dice than the spell's level get a Fort or Wil save--whichever's higher--at -2 per spell-level. Success still does damage at 1d10 per spell level. Almost always fatal to same-level creatures or one higher.
Or, the wizard gets +1 per spell level to a Charisma check, versus a Will save for the potential victim at -1 per spell level. Spell-resistance X gives that number as a bonus to the save, but the wizard's level can mitigate--doesn't come into play, otherwise--the resistance. Immunity is not as broad-range, and has levels, completely stopping the effects of any spells of X level or lower.
What do you think? Just spitballing, but the above is sort of the idea I had for modifying existing spells.