I like the mystery - not all mysteries need to be explained. Audiences can put in their own personal fanon. And Guinan was shown as being on a plane not unlike the Q,which introduces even more mystique. Some of it might be romantic, some of it might be something most humans can't fathom. I prefer the latter; any soap opera can go into romance and that gets boring very quickly and is the antithesis of the mind-expanding nature good sci-fi should be (IMHO, YMMV).
Whoopi was a big name back in the day yet she's playing a crewmember. There's no loud pomp, she's just being humble and part of the whole inclusive group (though it's still true Guinan is far more than a mere mortal human). Actress like character, there is something much bigger behind both... but she's not Q, who is as much an opposite of Guinan the way the Borg is to the Federation. Both have some certain similar traits, but how they are used.
They did throw things at the wall - which adds to the intrigue. It bugged me more than "Generation" tries to answer it but it was all so haphazardly done and cheapens it all, even adding continuity problems into the fray (Borg in Federation space when the Federation was a smaller size??)...