Perhaps we could restrain gods' area of influence to a zone around where they have a priest of themself, meaning someone who has decided
alone to completely devote his life to a god.
This could lead to some cool situations :
- A migrant priest of Fire coming to your fortress where the dominant religion is towards the goddess of Plump Helmets, Alcohol and Parties. By coming, his god could start acting in your fortress, so you'd probably want to make him see how hot is magma before a civil war breaks out.
- When under siege, the enemy will have to bring at least a priest of their god so as to be under his protection (if it pleases him to do so). So you'd have to kill the priest first - just in case.
- It would be really meaningful for a civ worshipping a minor god to flee somehere where there is nobody from another religion : there, they could live in peace, far from gods' wars.
I was thinking, about the motivations as a god : being a god, you'd more or less like everything to be up to you, so that the world would be your ideal world. This is a reason good enough not to want other gods to mind your business, except if their vision doesn't bother yours.
OR, as it's been suggested above, prayers and denial of their sphere of influence could cause them pain. They could make pain disappear by satisfying prayers or making people do more jobs related to your sphere of influence.
In any case, gods would like to see jobs related to them done. When a dwarf is sad, he could do one or several of these jobs hoping his god will bless him.
A god wcould like his followers protected, cause they help him (either in making the world the way he wants, or in handling pain), that's why he'd want them to believe in him and why he'd want to protect them (because if he doesn't, they won't believe in him).
On the other hand, an extremely sad dwarf would be angered at his god, destroying things the god is related to or turning his will to the opposite of his former god (and, perhaps in rare cases, becoming a priest of this opposite god, thus unleashing chaos into your fortress).
Yet, dwarves taken in a godly crossfire would want gods calmed down, so they could do sacrifices to them, please them, or just kill the priests if they ant (this could be cool once grudges are in - one dwarf that everyone hates because he made the god of Chaos, Madness and Indecency enter the fortress the day his dog died)
So, a god's blessing is more likely to happen if your dwarves content him, and a god's curse is more likely to happen if you don't content him, or worse content another god he doesn't like. Yet, in this case, the latter would protect you from other gods.