Wow, there's a huge cliff between using a themed control, and using an element - so I dug around in the yahoo code and found that the problem with PageIndicator looking odd at different widths could be fixed with a single line, by inserting this into the renderSkin method of the theme:
CODE
ff.lastChild.width = w;
I've defined a subclass of KONtx.control.PageIndicator with its own theme, which is a workalike to its parent, but has that one line that scales the "shine overlay" image to fit.
Personally, I think it would be great if the standard control scaled itself, although I've gathered there's a strong resistance to scaling images for any reason. Is that related to the processing power of some devices? I haven't gotten to the point of trying my widget on a real device yet.