I am almost totally in agreement with you on your review. Of all Beatles songs, I have the most personal affinity with it. So I'm somewhat protective of it when someone offers a lame interpretation. Fortunately, there is little that you and I disagree on. But for the sake of carrying on a discussion, here are my thoughts:
"Beautiful People" - Having lived through the 60's (and still remember it), the so-called "Beautiful People" were, in fact, those people before the pretenders (or plastic people, as we used to say) took over. Essentially, they used various means, drugs or otherwise, in search of enlightenment, comic consciousness, or whatever term you might choose. John, at the time he wrote the verses for "One Of The Beautiful People" might very well have considered himself one. Here's an analogy: Compare the 1967 Monterey Pop Festival with the 1969 Woodstock videos. In two years, LSD had become a recreational drug instead of a path toward some spiritual growth. Both John and George would become disenchanted with the "Beautiful People" later in 1967.
Yes, Brian did go through changes in late '66/early '67, not unlike the Lads, and that includes his first use of LSD. And so, John's verses included questions asked of Brian, as a way of welcoming him to the "Beautiful People." Questions like "How often have you been there?", "What did you see when you were there?", and, "Now that you've found another key, what are you going to play?" If you have the time and patience to track down druggie slang from the 60's (not the 70's), the word "there" referred to that state one reaches at the height of an LSD experience. "Far as the eye can see."
Mick Jagger - in a 1993 interview, Mick confirmed he was there and joined in at the coda. I don't hear him, but I'll take his word for it.
Clavioline, yes. Oboe, no. Too many people think Brian Jones played oboe on this track. They must be confused with his playing sax on "You Know My Name." Even if Jones was there, no way could he play oboe that well. Yes, he could "play" many instruments, but in my humble opinion, he wasn't that great playing the recorder, dulcimer or sitar on Stone's tracks. He was okay on sax, but only because it was his first instrument before guitar and blues harp.
Paul's chorus - It is true that Brian Epstein was a rich man (too), but that's not enough. Several references to Brian's "bag" appear here and there. The only reference to a brown bag was connected to their last world tour, which included the Philippines. Yes, Brian carried the concert receipts in a bag. It is also rumored that he carried the Beatles's drugs in the bag. Supposedly, the Beatles were delayed after the "Marcos snubbing" from leaving Manila. Both Brian and Mal Evans were forced off the plane, and according to the story, Brian was "relieved" of his brown bag by the authorities before he, Mal, and the Beatles were free to head to their next stop, India.
Zoo - Pure conjecture on my part: Zoo, besides being a convenient rhyme with "do" and "too", could also refer to Beatlemania, in general, much like John's description of being in the "eye of a hurricane". Picture the Beatles locked up in hotel rooms, allowed to come out only for public appearances, like animals in a zoo. Better yet, what if the zoo was the Manila airport where the Beatles (and Brian) were pushed around and beaten by the soldiers like animals? Or what if the animals were the soldiers themselves?
So, "You keep all your money in a big brown bag inside a zoo, what a thing to do". Could this be Paul's way of saying, "Thanks, Brian. for going through all that crap for us?" Remember, that incident happened less than a year before and was still fresh on their minds.
Now for the tag at the fade out: People who listen to the track today claim they can't hear it. I don't blame them. I can't hear it either. But I have one advantage over them. I bought the mono single, first pressing, the day of its release in July, 1967. On the first play of the track, I HEARD it. Clear as a bell: "Baby, you're a rich f** Jew". Only one voice speak-singing it and it sure did sound like John. As much as I DON'T hear it today on the 2009 remaster, that's how much I DID hear it in 1967. All you have is my word.
On subsequent remixes on vinyl (MMT, YS), it is very muddled...VERY muddled! The consonants don't pop out of the speakers during the fade. On the 2009 remastered version, it is almost non-existent, even if the vocal track is isolated.
To rap things up, here's my theory, take it or leave it: Both John and Paul decided to write a song in honor of Brian. Starting separately, they wrote their parts, compared notes, and saw a way to meld the two. And to make sure Brian would be absolutely sure that the song was about him, John threw in one of his anti-Semitic, homophobic jibes at the end. Brian was accustomed to that verbal abuse from John in the past. Vicious by today's politically correct standards, but typical for John and his friendship with Brian.
Why the change? The song was released in July, 1967 (and I bet it had Sir George's approval). Brian died in August, 1967. What was regarded as a private, inside joke in July was probably considered tasteless by the end of August. Thus the gradual masking of the "rich f** Jew" line over time. Compare the length of the original mono vs. the stereo mix. Nine seconds difference. Hmmm. Only with modern digital equipment could the line be virtually eliminated.
By the way, I'm willing to consider other theories. For example, Al Brodax, producer of the Yellow Submarine movie was at that session and claims the song was about him. Why? Because he had a brown bag with him. Take that with how ever many grains of salt you desire.