Making it a 1-tile AoE would actually destroy more tiles. It should be noted that I pre-cast because I didn't want to wait for the Elemental Lords to wander outside of their Wildland on their own, so I baited them. But you don't need to pre-cast, you just need to cast on an tile adjacent to an Elemental Lord, then move on that tile and attack the Elemental Lord. As I said, it's basically one tile that you will lose and I think that tile can be turned back into a normal tile by an outpost/city.
As to the second point, I've mostly attack the Elemental Lords myself in the testing, I don't remember the Elemental Lords attacking me (Because when they did, it was usually at the wrong time and I would use cautious to exit the fight and move them closer to my trap). That being said, casting on yourself (The few ways I tried, kills you). The spells that served as an inspiration for this are Curgen's Volcano (Hence the destruction effect) and Salt the Earth.
I see; what I meant by AoE 1 = 1 tile, with no surrounding tiles (i.e. what it apparently already does.) I was mislead by your previous comment, and thought that it had a radius of 1:
I could not change the tile where Vetrar is (Spell limitations) but I changed every tile around him to make sure -I- would be on a Northern Wastes tile when I initiate the fight.
...and you might want to explicitly point out in the first post that you can't cast it on a tile your unit occupies or it will kill them.
Interesting that it kills you - does Salt the Earth kill units in the affected tile? (I've never cast it). Seems like it would be unintentionally overpowered if so. Also - because of this side effect - you probably want to set the AI probability really low so it doesn't instakill you with it (though I've never seen the AI cast terraforming spells, so not sure if it's something to worry about.)
Possible idea for future mod: if you can find some way to make the "added" tiles convert when the "main" wildland does, this could potentially be used to allow wildlands to grow, either over time or in response to some event.