Truth be told, I am not sure how you guys handle objects within the game, and how each of those object doesn't cause chaos on the server.
My suggestion would be to only allow one Campfire at a time. Require the player to "PUT OUT" the fire and then "Destroy" it. Only then should they be able to rebuild another. I know the Campfires are not mega graphics intensive but they still take up space and make the land look bad when there are to many.
Also I suggest; which I will just assume you will already do, that you make a Fire-post, or lamp light for cities when they become available. That way you can illuminate cities and only within those limits or within post limits, and keep down Campfires.
I know I deleted a toon after putting down a Campfire and it stayed there afterwards and is still there that I know of.
Oh well just my two cents.