By default a single click expands the album tracks, so i dont get why anyone would additionally need the ability to double click to acheive the same.
And if you disable showing the tracks on a single click, then the option to double click to show the album tracks is still there
Well for me personally the single click was really for playing purposes. To open an album and select tracks, or see how far into the album I was . Also just the nicety of seeing the album art more largely in a coloured preview pane.
I used the 'album and artists' view for editing purposes, usually in my inbox, to 'auto tag by album' and such (especially since it sometimes didn't work in the main view). In fact, the reason I just recognised this had been removed was that I couldn't select 'auto tag by album' from the expanded panel view. I've since taken the advice you gave above, removing the expanded panel and instead using double click > album and artists, and it worked.
My preview settings were also very simple, track names, times, and thats it. The album and artists view I had a lot more detail in columns such as bitrate, file location, etc.
Anyway, I just think it was an elegant way to have a good looking simple preview for playing, and an easily-accessed more detailed view for editing.
Edit: Just to add another reason, in this current form where I need to click through each time to check an album's tracks or access things that were previously in the right-click menu (send to, tagging, etc), I'm basically going to have to hit the back button a lot, or use the right click for pretty frequent functionality like playing a specific track within an album. It makes browsing through my albums much clunkier than before, where having the expanded panel for quick playing, browsing, looking at individual tracks was so much more efficient. Especially across a large collection (and with as fickle taste as me!)