Perhaps the Spark is a sort of a Ley Lines thing? Essentially, the Spark is the energy of the planet itself, as manifested in people. Those like the Heterodynes and the God Queens have found a direct link to the actual source of the planet's energy (the Dyne being a naturally occurring Ley Line deep beneath the surface). Hence the "safe power source" being that since the Sparks derive power from the Earth, they won't lose their buffed intellect unless they somehow leave the planet or the relevant aspect of the Earth is weakened.