Humanity is on a world the suffered a serious mishap with Terra-forming technology. The main reason I believe this? Vatteries. The growing of meat like a plant, the crystals which behave like intelligent computers.

Etherialists are the remnants of Builders that chose to remain behind, the Builders who left are some form terraforming corporation. The spires are basically what the builders who remained used to survive in with the rest of humanity.

Folly Spoilers
Actually this whole book reads like a Steampunk version of the old series of Star Trek. Including Scotty Give me more POWA!

I love it.

Also the way rusting takes place so quickly in the books as its suggested in the matter of days affecting the entire object in question from just one little spot? That just speaks to me of some airborne effect that was used to terraform the planet. It also explains why blood causes the creatures to go nuts since it contains oxidized iron from the hemoglobin.