Thanks for the tip, but this doesn't seem to work for me. The value of readingLineHeight was 1.3 so I changed it to 1.2, ejected and powered the device off and on. But the spacing didn't change and upon checking the file I saw it had been changed back to 1.3 again.
However it seems to be that when I do an epub->epub conversion with calibre stripping the line-height terms from the .css, the line height can then be adjusted, but the minimum height is much more than 1.3, it is more like double-spaced.
Has anyone managed to convert a book that didn't allow the line spacing adjustment into one that does allow adjustment, and allows the spacing to be set to normal (1.3 or so) spacing? If so could you post a link to the .epub so I can try it out?