Thinking about doing some math on when these spells are the best to use, and wanted to see if people have given this thought:
1. Wait until level 4 portals - more portal capacity means more goods from each spell.
2. Use right away to power-level portals - portal at level 4 for longer means more overall goods.
3. Use to unlock key techs.
4. Other/combo?
#3 is very situational. I am envisioning a tech that either (a) really boosts your city [like a residence upgrade] and/or unlocks 4-5 other techs to fill [if you don't want to be tech-locked and fill AWs]. I could see this being Sentient Good/Tier Factory upgrades, a prestige building tech that would let you upgrade lots of traps/golds, or something like that. My gut says that it would be rare, though.
#2 This will be the hard math, and the way I'd think of it is two ways:
First, for "regular guest races" assuming that you have an ElvenGems recommended build. Then trying to figure out the per-day production (and aggregate production) based on total goods required for a particular chapter.
Second, for "limited space races," like S&D and Amuni where a portal upgrade unlocks not only more productivity, but also more buildings that produce goods.
Complicating matters, as I think
@SoggyShorts pointed out, is that with path #1, you might now have enough spells/goods to then delete all or most of your guest race buildings. So how do you value the extra space in your city now? I think the comparison then can only be "fastest way to produce required guest race goods," because you're either getting free city space at the front end or the back end.
Every chapter will also have complicating matters. For instance, mana/seed costs for techs, gold/supplies/tier goods for portal upgrades. There's no good reason to power-level a portal with guest race goods if you are stuck waiting 2-3 days per upgrade for sentient goods, for instance.
Thoughts?