Yeah, extended view would probably be a good use for the mouse.
Though I'd really like the ability to quickly move stuff around with ctrl+arrow for smaller lists.
Context-Menues are actually very useful for keyboard-users, too.
On a Windows-keyboard (is that a word?) there's a dedicated button for it.
I use that for accessing less often used functionality like "duplicate Thought",
which isn't worth having a keybinding for, but is convenient to access via context,
arrow keys and then enter.
If I could only highlight a link, I could use that key to do most of what I'd want with link types.
[like actually using them]
Isn't there a context-menu/Apps-key on a Mac keyboard?
Maybe that could work for you as well. (the Apps-key opening the Attachment context, when Plex is not focussed, I mean)
"Show in Explorer" would be "Show in Finder" (I think)
Anything you see in a dialog like this can be mapped.