Thanks for the reply Stephen
What I'm doing is building a set of generic templates that contain all relevant functionality, and are nicely styled right out of the box. Then I don't have to spend time building new templates every time I use the store. The relevant functionality is lifted from all the other stores I've built over time.
The intent in this case was to display the category image when the category is viewed, not just when the parent category is viewed, as it is now. This would work in conjunction with the category name and description to provide a descriptive header section for the categories. Obviously one could insert an image into the description editor, but re-using the already-uploaded category image makes sense. This particular store that I am building my generic templates on is transferring from a zencart site which does exactly this.
Obviously if the image is only a small thumbnail then it's not necessarily useful as a full header image. Perhaps it would make better sense if it allowed both a category thumbnail and a category header image to be uploaded.
However, it's not a huge drama if it can't go in. I have a long list of notes I recorded from the build of the first site that is now live and I will be sending those through as a series of bug, suggestion and request tickets in the new year. I can put this one in as a suggestion at that point, and I'll examine the remaining data and see what else would make sense alongside it.
But I won't hit you with all that this late in the year :)
Thanks
Rob