In the context of "restoring the game to what the designers actually wanted", I really don't think having Intelligence affect the base damage range of spells (much less the healing range of CURE spells) is a good idea. The only justification for the idea is that it's what the GBA version does, but the GBA version is a radical "reimagining" which changes the game's mechanics in all kinds of fundamental ways, even changes the conceptual roles of some character classes altogether (e.g. making the Thief/Ninja a "lots of weak hits" guy as opposed to the "fewer but stronger hits" Fighter/Knight), and all the while deliberately reproduces at least one of the original game's most balance-altering bugs (namely, the critical hit bug)
Having Intelligence directly affect spell damage just doesn't gel with the way FF1 treats stats, which is that each stat is used in one and only one formula. Strength affects Damage with weapons, but it doesn't affect Hit % or Black Belt Damage (which is a different formula from weapon Damage). Dexterity affects Evade %, but it doesn't affect attack order or Hit %. Vitality affects HP, but not defence (Absorb), magic resistance or status recovery. Luck affects running away, but not critical hits or Evade %. The only exception is that surprise is affected by the lead character's Luck and Dexterity, but that's also exceptional because it's the only formula in the game that uses two stats. If you consider the sum Dexterity+Luck to be a sort of sixth stat, then surprise obeys the same rule as everything else (yeah, yeah, special pleading...)
Anyway, based on this observed rule, we can conclude that Intelligence should affect either the magic "Hit %" formula or the damage of damage spells, not both. And to me the former makes a lot more sense, if for no other reason than because in FF1 magic accuracy "needs" a boost a lot more than magic damage does. In the original game without any bug fixes, damage spells continue to be somewhat useful throughout the game, but status and instant-death spells start to seriously suck around when you get the airship, if not sooner.
Also, for what it's worth, none of the earlier CRPGs which this game may have drawn inspiration from had spell damage increase in proportion to the caster's stats. In Wizardry and all its imitators (including Dragon Quest) each damage spell inflicted a fixed range of damage, and each healing spell healed a fixed range of HP. And no version of D&D, ever, had the damage of spells like Magic Missile and Fireball be affected by the caster's stats (level, yes; stats, no)
Oh, and on the subject of D&D, a lot of the comments I read in this thread are way off base. The commenters here don't seem to realize that the D&D that anyone younger than their mid-20s is familiar with (D&D 3rd Edition) is, in terms of mechanics, a completely different game than the D&D of the 1980s which this game and all the classic CRPGs were based on. And one of the biggest differences between new-D&D and old-D&D is that new-D&D places a lot more emphasis on ability scores than old-D&D did. The suggestions in this thread to have practically every magic-related calculation in the game (damage amount, healing amount, spellpoints gained per level, even the chance of an enemy waking up after SLEP) somehow relate to the caster's Intelligence in order to be "more like D&D" are certainly coming from people who only know 3e, which is not the D&D that Akitoshi Kawazu knew and played at all.
