Nick, thanks for the fabulously written review. I share pretty much the same sentiments regarding Rattle's BPO M7. I like the pacing, and the playing is great, but there is definitely such a thing as Mahler that sounds 'too good,' which is not all that common with other composers. Another one I can think of off the top of my head is Shostakovich, and it makes sense because Mahler and Shostakovich are very similar composers. You want your Shostakovich to sound tight and exciting, but not too clean; it needs that bite and snarl.
The Rattle BPO M7 is very nice to listen to, and I can possibly recommend it to a first-time listener in order for them to get a grasp on the musical elements, but for a serious recommendation on Mahler's characterful intentions one ought to stick to Bernstein, Abbado (Chicago or Berlin), Kubelík, Chailly, and Gielen. Probably Tilson Thomas with the LSO too. I don't like Chailly's finale all that much, but that's just personal preference. I like a faster, rougher, naughtier finale as opposed to the more steady-handed regal approach.
Some recordings that are refined can work really well, in my opinion. Those are Zinman, Vänskä, Nott, and Dudamel. I think the trick here is that the orchestra members have to actually still try to play this difficult music, as opposed to the Berliners who could basically play this music in their sleep.
Oh, and Stenz still has the best finale of anyone.
By the way, as far as Mahler 7 goes, has anyone heard the Tabakov recording? It's rough, gritty, admittedly not all that well-played, but exciting as hell. One of the best finales I've ever heard, clocking in at 16:28. Like I said, the playing is not perfect, but it has a lot of character and you can tell that the Bulgarian musicians are playing like their lives depend on it.