I often browse through my (fairly) well organized collection of MP3's, and there's one feature I still miss in the MP3tag. I'd simply like two buttons to navigate directly to the next and previous folder in the folder tree. I'm not very happy with todays open folder dialog, it requires a little to much mouse clicks. And I'd also like the files to be selected (or at least a select all button on the toolbar) when I open a folder with MP3's in it.
I like both of your ideas. Usually it's just faster and easierr to exit Mp3tag and then use Windows Explorer for navigation and the context menu to relaunch Mp3tag. That alone is a pretty telling commentary on the built-in folder navigation (but on the good side, also just how fast Mp3tag loads).
A button for Select All would be great.
And speaking of buttons... How about a customizable button bar? I've never used 1/2 of the buttons that are there. Another idea would be able to be able to create custom buttons that could be attached to Action Groups. Display the Action Group name on mouseover as a tooltip.
Fantastic program, but the user interface could use a little refinement.