I am already planning to add support for multiple source directories. Not sure when it will be released, though…
Your second idea is interesting but I am not sure how it would be implemented in practice. For example, if you add a directory, then Gallery Server Pro will import it and its contents. Then maybe you decide to delete a few images from Gallery Server Pro, which will delete your Gallery Server Pro copies but not the original ones in your reference directory. So far, so good. But then the next time Gallery Server Pro checks your reference directory, it will pick up your previously deleted items since they are not currently in your gallery. There are other difficulties when you consider how to handle items that are moved or copied in the gallery. I am sure it can be done but it might be pretty complex to pull off.
Roger Martin
Creator and Lead Developer of Gallery Server Pro