I haven't explored the subject theme skins enough, but keeping your cutting up of graphics to a minimum definitely makes things easier.

I believe multiple sets of .rc's and graphics files to be the better solution. That way you can just create a new theme skin whenever you feel like it, without having to walk through your theme configuration updating if-then(s).

A theme skin in this case would be graphics for all your components, and some .rc containing evars for common settings to be consistent throughout theme components, such as text colors, font sizes, component borders, background drawing modes...

I don't know if this scheme has ever been used by a theme, if the reason is that modules don't necessarily skin themselves the same way (e.g. taskbar3 vs. label) in terms of graphics requirements. Another example is that it may be the case that some modules take point sizes instead of pixels for font sizes.