Peter,
If you are still interested... I am going through the same exercise and have found a happy median with Zenfolio. I have Galleries set up by theme for Landscapes (with various sub-categories such as coasts, mountains, waterfalls, etc.), Nature (w/ sub-cats), Travel (sub-cats are identifiable places, so previous photos may appear again), etc.
The feature I like as a corollary is the search function, to allow users to put their own keywords in, so they can ignore my categories if they wish.
Maybe I'm alone in this, but one thing that bugs me as a viewer/user is when I see the same photo again and again and again on the same site, but under different categories. To me, it says the photographer doesn't have a lot of depth, so I am working hard at not having the same photo in more than two (rarely three) galleries/sub-categories.
Terry