I agree with just about everything you and Drummer Chris have said, FoxHound.
IMO the Stones peaked with Exile. By all the recent accounts about the making of Exile, it was a far more difficult period for the band than I ever realized. While I like Goat's Head and IORR quite a bit, they are definitely not as good as Exile - perhaps the Stones were still feeling burnt out when they started working on Goat's Head (the prolonged use of heroin and cocaine was no doubt taking its toll also).
I think a big part of the Stones rougher, heavier sound in the late 60s/early 70s was their producer Jimmy Miller. The first thing he produced was Jumping Jack Flash and his last album with the Stones was Goat's Head Soup. Supposedly he was a burnt out junkie by then. That could have something to do with the decline in quality of that overall album.
IORR was the first album that the Glimmer Twins produced themselves, and it was the last one with Mick Taylor. He quit in the middle of it, he only plays on 7 of the 10 tracks. That is one reason that this album isn't stronger.
I agree that the Stones had a great comeback with Some Girls - while not as technically proficient as Taylor, Woody was a good replacement.
Even though the Stones albums from the past 25 years or so haven't been as good as their earlier stuff, there are gems on every one, and I think all of them are worthwhile efforts. Some of them are great.
I hate to say it, but I think Woody has been carrying Keef when they play live for several years now. If you play close attention to the dvds Shine a Light or The Biggest Bang, Woody is often playing Keef's old rhythm parts while Keef noodles over it. Not on every song, but on a lot of them.
Word has it that Keith has arthritis pretty bad now and that's been hampering his playing (and some of his songs are a real workout for your left hand, particularly Brown Sugar..after 3-4 minutes of playing it, my hand always aches!)
I still think Keef is the riff-meister though, he is rock 'n' roll.