Many thanks Miro. From what I've tried, the outlining features in Notecase would be an excellent starting point. I'll be in touch later.
Regarding Writer's cafe:
I read sooooo many reviews of Writer's Cafe last night.
Based solely on the reviews I read, it seems an excellent plotting tool, which could be helpful for me, but only at a later stage.
Right now I am generating ideas by the ton (some plot, but mostly history, location and technology notes). My many paper note books are now struggling to keep this organised. An outliner is my preferred choice (my brain just happens to work that way I guess), but the reviews imply an outliner is not provided in Writer's Cafe. It is hard to be sure, but its note taker does not seem to provide me with the ability I want: to expose ad-hoc relationships between notes.
When a late-but-exciting idea turns up (as happened a few days ago), several old ideas need to be adjusted. Changing these invitably requires changes to some others, and so on. The full extent of the ripple depends on how the old ideas are related ... if only I could easily see these relationships.
Somehow, I don't see Writer's Cafe helping with that.
Unless any new suggestions turn up now, we're probably near the end of this thread. So, I'd like to thank you all for the excellent help and discussion on this subject. It has been a truly remarkable experience.