@davidfor,
Yes, I know how to force ToC items for my own html-to-epub calibre conversions (I use the <h1 title="Map"></h1> option) but I seem to spend a lot of time fixing up existing partial ToCs or sometimes totally messed up ToCs. Sometimes it's just faster to throw away the existing version and create anew from the 'generate from files' option.
Speaking only for myself, I'd be perfectly happy with an auto-generated entry of 'Untitled' (or the filename) for any file which doesn't contain any text. It can easily be edited later and it's faster to manually delete unwanted entries afterwards than to have to search for possible 'no-text files' which have been auto excluded.
... or maybe I should just spend less time
fixing and get on with the actual
reading 