Yeah, :/
They end up stop generating about 500 blocks away from spawn or so. It's different in the different directions. I think East they stop in 500 and north is about 1600. I've got a good idea in my head to get some more gold hopefully it will work.
They do not stop. If you are playing the old map then there is a large blank spot on the map to the north west, and a small blank strip to the south, but other than that it goes on forever. The spires and bunkers and such are all "ruins" and they are part of the world gen. If you are not seeing this then there's something wrong with your world.
There's also ore in the chasms, pretty sure there's a bit of gold in them, also some diamonds and silicon. A normal mob farm will get you a decent amount of gold from gold tools and armor. Meteors are the best source with a fortune III hammer, better than spires.