I'll try to keep my reply as non-spoiler-y as possible ;) There are a fair amount of "minor" mysteries like this one that are clearly just waiting for the right time to be revealed. I suspect that there's a future showdown somewhere near the end of the series in store between Smoker & co and the Strawhats, and we won't find out what exactly is going on with her until then...

On the other hand, there are bigger mysteries, like the other thing you've mentioned, where it's more like a giant puzzle, and we get pieces to it on a regular basis; small parts of the puzzle get solved, but new unsolved sections appear, and the overall picture just keeps on getting more and more interesting =)

Ah, when you get more caught up, maybe I'll have to dust off some of my old articles on some of my theories^^ (<3 this show so much)