Having gotten to the point of being annoyed by the way that WinZip overwrote the association, I finally crawled around the web to find a way to restore the CompressedFolder functionality as a more convenient method for reading, even if I want finer control for writing.
Most places talking about this are mildly dodgy, want to have you drop massive slabs of stuff into your registry or say "re-install your OS". Fortunately it's easier than that.
regedit, and go to
HKEY_CLASSES_ROOT\.zip and change the
(Default) value to
CompressedFolder. That restores Explore as the default option, which was what I was after.