I had been working on a magic mod, but I never finished it. I did use it in a single test game though. Unfortunately I have not had much experience with the late-game "Omega" spells. For example I've never actually experienced Murdering Winter, Haunted Forests, Armies of Gold, or Astral Corruption... so I can only analyze them theoretically (from reading threads, mainly), which makes them very hard to balance accurately!
I think it does quite a good job on the early-game summons - stronger, cheaper, less hungry, and so forth - but I never wanted to post it until I thought it did a good job on
all magic spells. Too bad, because it gives a neat new descriptions to each of the foul spawns
One way that the AIs in Space Empires 4 and Total Annihilation were tweaked was to create AI-only technologies and units that compensate for concepts the AI cannot understand. In Total Annihilation, for example, the AI would never build nukes, even though it built silos - so it could never launch nukes. The solution was to make an "AI Nuke Silo" that did not need nukes built before firing; it just automatically reloaded itself every few minutes.
In Dominions II, every nation (not themes, unfortunately) could be given a commander type that generates surplus food. If the commander is cheap, the AI will automatically build them, and keep them with armies... the player simply has to NOT build them (or disable them for his own nation). Or there could be one mod per nation giving all the national leaders surplus food, leaving the player to enable the mod for each AI nation that will be in the game. Hmmm.... yeah, I like that version. Unfortunately, it will make besieging the AI much harder if they never starve.
Well, I'll think about it a bit. I'm attaching my magic mod to this post, if you want to look at it... it does NOT make vine ogres stronger =)
p.s. I should note that it contains every spell in the game and (IIRC) most of the summoned creatures in the game, with complete (usually modded) stats.