I like the basis of this idea; probably more like Ancient Greeks felt about it, wondering in which mood gods were and if they were on their side. And yeah, seeing the gods changing faces would be fun
But more things need to be put in it to have it in use often enough (otherwise dev cost would be hard to justify).
I don't know if you've experienced a big account in a speed 3 world; then, you get 500 favs maximum so quick, it's so long to build a myth nuke when you can simply queue classical units everywhere, when you fight someone of your size it would probably be like 30 attacks in a row, only 4 of them can be spelled because of favor cap, etc... In the end, favors look like a little plus you always have under hand but which is rarely important.
Most players have most of their days without any battle, they'd see their gods always happy from simple happiness per hour.
The way you put it, someone winning a battle gets a plus in favors (the player will care about battle result and not bother his favors being raised), someone getting his myths killed during sleep will have a minus (and it will be even harder to rebuild the nuke). Not sure it helps the dynamics of the game...
You could have other things like, for example, possibilities to spend standard amount of ressources in temple for a special celebration honoring this god, getting a plus in favor production. These celebrations could be launched from gods overview too, with a button next to each city. This would help building myths quicker.
At some point, you also need to do something about the 500 favors cap, otherwise big accounts won't care at all about it. It would be quite natural that your favor cap raises by step with the total size of you temple.
If you raise 500 favors cap, you also need some securities to avoid disbalances. For example, sea storms could only be launched a limited amount of times per hour. Otherwise, someone close to losing a city could, instead of fighting, rely entirely on this spell to sink CS, and it would be unfair to the attacker.
I'm not sure gods should care about their myths being successful or not. They're gods.
For the minus, apart from temple leveling down... for example, you could use favs (neutral) or make celebrations (good), but if you do none of this for a certain amount of time, fav production slowly decreases. If you show no interest for a god, this god won't care about you.
So, my input, to be discussed:
- Raising fav production can be done naturally by upgrading temples, but also by making special celebrations in temple to honor this god.
- Your favor cap for all gods raises by steps with the total "spiritual power" of your temples. This is balanced by limitations for some spells to avoid abuse in battle.
- Minus in fav production from temple losing levels naturally, or with the changing god penalty, or by not using its favs and not celebrating this god for some time.