In re-reading through Aeronauts Windlass, I had a thought.
Everyone or it seems its common to all to have some minor telekinetic ability while Etheralists have major ability at a high cost.
Consider this, crystals are turned on and off by personal will. Over time crystals become less sensitive to individual's level and can only be activated/follow the mind of an etheralist.
For the spires, it sounds like they keep a higher than normal O2 ratio, which makes sense in a mostly enclosed environment but I also think the etheric currents have something to do with the rust fears. This would increase the chances of oxidation in copper but more than that, the Spirestone is specifically designed to harness and provide clean energy for all. The nexues and flows of etheric energy follow specific pathways on their jouney form the top to the surface. The crystals absorb it. Also they have found a way to both contain energy in crystals and release it. Note the different types of grown crystals - lift, power, trim, gauntlets, and lumin. Yet as Folly explains they are based off the same core concept. It also explains why the old power crystals get better over time. they are naturally grown and with the constant power fed to them grow, and reshape itself internally to become more efficent. I think the original power cores like the one in the Predator were found, not made and it was from them that was how the templates were made.
