Let's look at a few of the spells that have been changed and see. I'm only looking at the damage-dealing spells, since that seems to be the main focus of this spell revamp. I'm going to list the damage they do at various caster levels.
(scroll down if you don't care about the numbers)
Single-Target Spells Effectiveness at Various Levels:
Scorching Ray: 20 avg damage per ray. 6 sp.
Melf's Acid Arrow: (2d4 + 1/caster level) per tick over 12 seconds. 6 sp.
Frost Lance: 32 avg damage per ray. 8 sp. Fortitude save for half damage.
Burning Blood: (4d4+2/caster level) per tick over 12 seconds. 8 sp.
Disintegrate: 10/caster level average. 20 sp. Fort save for almost no damage.
Level 3:
Scorching Ray: 20
Melf's Acid Arrow: 8 per tick (about 48 total)
Level 7:
Scorching Ray: 40
Melf's Acid Arrow: 12 per tick (about 72 total)
Frost Lance: 64
Burning Blood: 24 per tick (about 144 total)
Level 11:
Scorching Ray: 60
Melf's Acid Arrow: 16 per tick (about 96 total)
Frost Lance: 96
Burning Blood: 32 per tick (about 192 total)
Disintegrate: 110
Level 15:
Scorching Ray: 60
Melf's Acid Arrow: 20 per tick (about 120 total)
Frost Lance: 96
Burning Blood: 40 per tick (about 240 total)
Disintegrate: 150
Level 20:
Scorching Ray: 60
Melf's Acid Arrow: 25 per tick (about 150 total)
Frost Lance: 96
Burning Blood: 50 per tick (about 300 total)
Disintegrate: 200
Summary:
Melf's appears to be a much better choice over Scorching Ray at higher levels than at lower levels. My suggestion is to stop Melf's from increasing all the way to CL 20. It probably shouldn't be used past level 10 or so anyway.
However, Burning Blood appears to be the king here, with crazy damage over time, no save, and huge total damage. It's a better version of Melf's Acid Arrow that only costs 2 more sp, but it deals double damage! It pretty much destroys everything but Disintegrate. Disintegrate might be useful here, but its save makes it a lot less attractive than Burning Blood. Even Polar Ray deals only about 125 damage at CL 25, and it's an eighth level spell!
But wait! I can Maximize and Empower Disintegrate, and it'll be more useful, right? Its sp cost is a lot more than Burning Blood, so it should make it more attractive when you factor the costs of the metamagics.
Max + Emp Disintegrate: 500 Damage (not too shabby), 70 sp.
Max + Emp Burning Blood: 125 Damage per tick (750 total), 48 sp.
Well, for a spell that requires a save, I'd rather not use 70 sp for a possible 500 damage when I could use 48 sp for a guaranteed 125 per second. I could use Heighten, but that would make it even less sp efficient.
But what about the multi-target spells?
Multiple-Target Spells Effectiveness at Various Levels:
(note: I didn't include the various cloud spells)
Acid Rain: (1d6/caster level) per tick over 8 seconds. 12 sp.
Wall of Fire: (2d6 + 1/caster level) per tick over 30 seconds. 35 sp.
Ice Storm: (3d6 + 1/caster level) per tick over 30 seconds. 25 sp.
Cone of Cold / Ball Lightning[/b]: 5/caster level average. 20 sp. Reflex save for half.
Chain Lightning / Otiluke's Freezing Sphere: 5/caster level average. 20 sp. Reflex save for half.
Level 7:
Acid Rain: 24.5 per tick (98 total)
Wall of Fire: 14 per tick (210 total)
Ice Storm: 17.5 per tick (262 total)
Level 15:
Acid Rain: 52.5 per tick (210 total)
Wall of Fire: 22 per tick (330 total)
Ice Storm: 25.5 per tick (382 total)
Cone of Cold: 75
Chain Lightning: 75
Level 20:
Acid Rain: 52.5 per tick (210 total)
Wall of Fire: 27 per tick (405 total)
Ice Storm: 25.5 per tick (382 total)
Cone of Cold: 75
Chain Lightning: 100
Meteor Swarm: 160 (from all four meteors)
Summary:
So, Acid Rain appears to do about twice the damage of Wall of Fire. At lower levels, Wall of Fire is pretty comparable. However, at the mid levels (when one would typically be relying on Wall of Fire), Acid Rain blows it out of the water. It has a lower sp cost, deals damage twice as fast, and (at level 15) deals almost as much total damage as Wall of Fire in about 1/3 of the time.
The argument could be made that Wall of Fire is a fire-and forget spell, since you can cast it and let it deal damage for 30 seconds. But wait! In that time, you could cast Acid Rain, wait 22 seconds, and cast it again. You'd deal more total damage for about 10 less sp.
Not only that, it appears to outclass Cone of Cold and Chain Lightning (both of which allow saves) at even high levels. Only Meteor Swarm deals reasonably close damage. At the level that these spells are used, Acid Rain is far to powerful to bother with anything else.
On the plus side, it appears that Wall of Fire seems pretty balanced in regards to the direct damage spells, but it seems to have a cost much higher than comparative damage over time spells. Also, it seems about equal to Ice Storm now.
So, are the higher-level spells any better than their lower-level counterparts?