THE BORDER BETWEEN TWO ELEMENTAL PLANES IS RIPE FOR EXPLOITATION BY INTERLOPERS

Elemental planes are boring because the environment is so extreme the PCs will have a hard time adventuring there. More interesting, as stated by others, is the border between two planes. Take FIRE & WATER.

The borderland would be STEAM and maybe as this elemental conflict rages a third party, dwarves, move in to build a city based on steam-powered everything. The elementals too embroiled in their own conflict are now slaves in these objects, structures, and mechanism.

And to add on top of this, since the planes have proximity based on belief and not actual distance, maybe this City of Steam is in conflict with The City of Brass. So even though they are planes apart it is easy to find gates from one to the other because they are believed rivals. Sorta like if New York and LA were as far away from each other as an inverse of their animosity toward each other.

So there are two policial factions in The City of Steam: The NEAR which believe an attack from The City of Brass is imminent and the FAR which seeks to eliminate knowledge about The City of Brass and deny its existence to keep it away (out of sight, out of mind).