I actually kinda like the little thumb "alexicons" but I have absolutely no reason at all that I do. I just like them. The only remotely rational reason I can come up with is that when looking at a very large list of files (such as songs all by the same artist sorted by album -- but not drilled down to the album-only level) you can now visually easily tell where the "album borders" are. This would make navigation in Standard View a small bit easier for me on my TV (where the text is sometimes hard to read).
Quite often, I'll be playing a large playlist (usually a View Scheme with a complicated smartlist style filter, with MC set to shuffle mode) but like to scroll through and choose a particular song every so often. Since my "Mix" View Schemes are so huge, I sometimes don't bother to Add (as next to play) but just double-click to start a new track -- and just let it re-shuffle the rest of the tracks. Visually discerning the album "borders" can make this task a little quicker and easier.
That's a fairly lame reason though. I thought the previously mentioned idea of making the tiny thumbs their own "column" (and adding a new "status" column with the old color coded icons) was a great one. That way, those of us who irrationally like the little buggers could have them, and those of you who hate them (but want the color coded icons) could have it your way.
I'd personally probably display both columns, though the color coded column would probably be off to the right (off screen) somewhere. I, personally, don't have any reason to have files on my media drives that are not imported into the library. I suppose if you have multiple libraries it could be useful...