#4, fewer clicks, would be welcome -- meaning, more key data and actions things closer to the surface.
One way to do this is to make key dialogs movable/dockable, so the user could arrange multiple actions/areas of MC to be viewable at the same time. And non-modal, so the user doesn't have to close one action to engage another. Allowing customizable direct access, as an alternative to nested menu navigation or hot keys, would lead to fewer clicks, and to the ability to work faster, and maybe be another "can't get this anywhere else" benefit. Image editing software is an example of this kind of UI.
This level of UI customization also would let MC be adaptable to the wide (and getting wider) range of users and therefore interesting uses, which might lead to more "big directions".
A key to customization is the ability to (minimum) have MC remember the position of everything between sessions, and (maximum) to have multiple custom screen layouts, same idea as views, zones, etc, since a screen/UI layout for library management would be different than for playing, audio different from video, etc.
For instance, when I'm in a heavy rip/tag session, I'd like to open and position a much larger tag window so I could see and click more tags at once. Next to it, a multi-line view of the library to again see most/all tags, but for multiple adjacent tracks as determined by the user (sortable, custom fields, etc), along with a look at the cover art -- everything at my fingertips, viewable all at once. But only for library management, so there would need to be other UIs for other purposes.