(I seem to have some trouble remaining logged-in for more than two minutes at a time.)
I think claiming it's 'the same album' is pushing it a bit! And I'm not sure I'd agree with 'steadily' declining after Astral Weeks. Veedon Fleece is up there with Astral, in my opinion, and perhaps even higher. And Tupelo Honey wasn't too shoddy. I'd say there have been periods of rapid decline, but also some reasonably stable periods. So rather than 'steadily declining' I think I'd go with something like 'fluctuating but with a definite downward trend'. (Not quite so pithy, admittedly.) However, from the heights of Astral Weeks and Veedon Fleece, there was only one way he could go. And as for his character, he's hardly unique in being a musician deficient in decency, is he? Mr 'Grumpy Boots' Zimmerman comes to mind since you mentioned him, and Nina Simone could hold a tune and give a tinkle on the old joanna with some aplomb but I wouldn't have liked to have been in her entourage. (Actually, that last bit's not true; I would have been over the moon, although probably not for very long.) Not that that's an excuse, but I think you can separate the music from the person, and it does perhaps make those who aren't so deficient a bit special. I don't think anyone ever accused John Prine, for example, of lacking in decency, did they? (See what I did there? Dragged this sub-thread back on topic.)
And, yes, great reminiscence, by the way.