My workaround (I guess) is to use two Smart Playlists which I've set to Grid view, with items selected by most recently added, and limited to 100 and 400 items respectively. The new global search in iTunes 11 allows you to search for and get to any of your playlists pretty quickly from anywhere in the app.
Of course, I'd
still kind of like to see an option to show album art in list view, and I hope they're getting lots of
feedback about that. Just a very simple
optional column for album art would be nice, maybe intelligently combining adjacent album art from the same album similarly to how the 3rd party app
TuneSpan does it.