I do think the Geisters may be a very rough, approximate "elf" parallel. I'm less convinced that they're in an alternate dimension where time runs differently. I agree that Lu's been gone a long time without being human: I'm still guessing she got herself tangled in a machine of some sort. Or possibly in a "Queen Bee." Or both: there's still room for "The Lady of Crystal" to be both Queen Bee and mecha.

I think whatever happened in Skifander it was at least partly a misunderstanding on Klaus' part. Zeetha mainly seems amused at the idea that she might be there to kill Gil. I'd tend to think it's one of Klaus' few, but horrible mistakes: he saw/heard something that led him to jump to a false conclusion.

Having Skifander and Geisterland both prove to be faery parallels works, though, as a literary trope.