One place where I think an error was made is in the spell point prices for Blast spells. Fireball and Lightning Bolt both do d6/level in pretty good-sized areas at 3rd level, while Cone of Cold does d6/level in an honestly-lousy area (cones are awful - you have to open a hole in the front line and expose your caster, and you're going to waste a lot of area most of the time) at 5th level. What gives?
The secret is that Fireball and Lightning Bolt both have "unpredictable area when used indoors, high probability of friendly fire" clauses - fireball expansion to volume, and lightning bolt random reflection off of hard surfaces. This hazard is borne out by that finest of accounts of old-school play: Tucker's Kobolds.
I recall we had a 12th-level magic user with us, and we asked him to throw a spell or something. "Blast 'em!" we yelled as we ran. "Fireball 'em! Get those little @#+$%*&!!"The hazards of using these spells indoors mark them as clearly "outdoor toys", to use my mother's phrase. Their availability heralds the wizard's entry into wilderness-adventuring levels, for use in blowing up large groups of humanoids in open areas, just as +1 hireling morale marks the beginning of the fighter's wilderness game (I wonder if there's an equivalent for cleric? They do get create water, growth of animals, and speak with plants all at 24kXP, 4kXP after wizards get fireball and 8kXP after fighters get hireling morale...). Further, because Fireball and Lightning Bolt are so dangerous to use, they should not trivialize dungeoncrawling, as we often see them do in later editions.
"What, in these narrow corridors? " he yelled back. "You want I should burn us all up instead of them?"
This friendly fire problem also explains the existence of Delayed Blast Fireball. I'm not totally clear on the history of this spells, but it does appear in Swords and Wizardry (an OD&D clone), indicating that it has some TSR lineage. The ability to delay a fireball, so as not to fry your whole party in the dungeon, raised the spell's level from 3rd to 7th. Swords and Wizardry also helpfully notes that the volume of a (20' radius, in contrast with ACKS' 10' radius) fireball is about 33 10'x10'x10' dungeon hallway cubes, which seems more than adequate to thoroughly self-immolate if used indoors, and makes it very clear the the fireball expands to volume. This is crazy; it suggests that the multiplier for "non-TPK-inducing" on Fireball should be about x2.33, and even that leaves you with another drawback (the delay)! If you just want some nice clean area effect damage that is blocked by walls, doesn't try to kill you, and does 1d6 per caster level right this round... too bad. There is no such spell in S&W (not even Cone of Cold with its crappy area). d6/level is serious business, and doesn't come without correspondingly serious drawbacks. Big areas of effect are a necessary consequence of dealing with that level of barely-controlled elemental energy.
Another illustrative example from Swords and Wizardry is Ice Storm. Ice Storm is 4th level, covers a 30'x30'x30' cube (but doesn't say anything about expanding), and does 3d10 damage, flat, fixed, no save. During my 3.x days, everyone hated on Ice Storm, but it makes a lot more sense now, because it is good for not committing suicide by sorcery.
In all of Swords and Wizardry, the only spells that deal uncapped one-die-per-level damage are Fireball, Lightning Bolt, and Delayed Blast Fireball, and they are all nontrivial to use safely and effectively indoors. The only other damage spell that scales with level at all (ie, isn't just fixed number of dice), that I saw, is Magic Missile, which scales comparably to how it does in ACKS.
Thus, while ACKS' spell creation rules explain Fireball and Lightning Bolt's relative advantage over Cone of Cold by research breakthroughs, I think an "if you use this indoors you risk a party wipe" modifier is probably much more correct. Honestly I'm probably in favor of just banning non-fixed-dice damage unless it's got some horrible rider attached to it. I also sort of want to bring back 20' radius Fireballs, too, because they are, from a certain point of view, more balanced than 10' Fireballs. And when a 20' fireball expands to volume in a wilderness hex because you ground-bursted it, you get a 25' radius, which lets you cover about 70% of a 60' hex. I'm not totally clear on how the maximum damage fraction for Fireball was set in Domains at War, but I suspect you could do a lot more than 1/8th of a Company's maximum HP if you covered most of its hex. Likewise, at Platoon scale, you could totally cover a single hex for excellent damage with a little splash out into adjacent hexes.