Well I'll be the first to admit that I loooooved Guinan. And I loved that they never explicitly explained her, her past, or her 'powers'. I agree none of it was likely intentional, it just happened that way, but I really like the intrigue it created.
Reminds me of listening to Nick Meyer's commentary on TWOK director's cut, explaining why the one glove that Khan keeps on his hand the entire movie is a small detail that is never explained, yet adds to the character.
Guinan was obviously a bigger deal than a glove, but I feel like the same applies. I love imagining what she and/or her race are really capable of.
Oh, one other note. I'm pretty sure Peter David was the author, of a trek novel from decades ago called Vendetta. It explored Picard's and Guinan's shared past, including with the Borg. First trek novel I ever read, and I recall really enjoying it. Should see if I still have it...