I liked that description of ghosts-echoes of once-living people. Many ghost stories that have multiple witnesses talk about the ghost going through the same motions, like the ghostly carriage that rides past one of the English castles over and over, night after night. Perhaps an electronic matrix caught in a magnetic field within a limited area? Who knows.
Indeed, and there certainly is some plausibility to this idea considering what we've learned about human biology. We know the human body is, essentially, a sort of electrical machine, and that's why electric shocks can often save someone having a heart attack. It also seems reasonable that a strong emotional catalyst, which is almost always the cause of a ghost, could somehow leave an impression on the environment. If this sort of energy transfer/looping can occur with humans, it could easily occur with other objects that are often associated as ghosts - animals, even technology like planes or cars.
* shrugs *

As I said before, there's a lot about the subject I don't know, and I can't easily answer. But I think it's fascinating enough to learn more.