Thanks. I though the ‘Views’ functionality of components was was a good fit for creating primary/secondary/etc variants of a button, as Axure even suggest this in their reference. But it turns out this is useless, because you end up with buttons that only allow you to overwrite the text, but you cannot change the resize behavior of the component (i.e. make the button auto-fit the text), nor can you resize a component instance, or put any interactions on it when using it (unless you mimic them all as events for the component). Okay, so components are out.
@axureboutique.com did show a neat trick in this thread though, by putting the components not in a RPLIB, but in a regular RP file, you can import and replace all instances in your RP design files, thus achieving what I think the aim of library is anyway. So shame that components are not suitable for core UI elements.
Still torn on how to proceed with creating a maintainable library of styled buttons in different variants, tabs, checkboxes, etc (essentially all regular form controls).