To paraphrase a quote from the late great Jeff Jones...
His response to a collector on the Comicart-L who had talked about trimming some "excess" border off of an original once. He indicated that said collector needed to keep his hands (and scissors) six inches away from artwork at all times. It was a bit of a goof, but the underlying intent was that if you really want to be a lover of art originals, you take the path of do no harm. Not unlike the medical profession.
There are instances of preservation that are not only welcome but warranted. But in the world of restoration and renovation for personal preference, Jones' inferrence was that one better keep their hands 6 inches away, lest they do something they later regret.
The kicker here is that it was the original creator that did the modifications. At the owners behest, of course, but still it was his hand. If he had a problem with it, he wouldn't have done it. Seems like he was into it.
If it were something I'd bought, I'd have kept it as-is. Simply because I am a lover of the process of original art as much as I am of the content of the pages. So to me, I'd never even think of changing the thing to suit my personal tastes. Same as I'd never give a page to Steve Oliffe to color, or cut out panels of my favorite pages and hot glue them to my favorite coffee table. And I totally could, if I wanted to. But that's not for me. I'm not in love with having a big representation of the published art on the wall. I could go to Kinkos with a clean copy of the book and make myself one of those for next to nothing. I'm into the OA. I see it as that simple.
I'm with Gene in that I just don't see this having any knock on effect to the Lee market, beyond this one page. It's become it's own outlier. Could go cheap at auction. Could be unsellable. Could sell just fine. But it's not like it's a piece of one of the greatest comic stories of all time, that's been rendered ash. It's one of hundreds just like it. Or near enough. But the creator drew over it. It's not like he had some uninvolved party to the book bust out the inks on it.
I'd never tell anyone else what to do with their possessions. But then I didn't shed any tears over those burned Ottley Invisibles pages. Or the time the post office totally crushed (I think it was) an Archie page. Mostly cause I'd no interest in that stuff anyhow. Now if a well know collector of a certain title like Saunter Lee was having Jill Thompson watercolor all of his Sandman pages, or using them to decoupage his bathroom, I'd have out the pitchfork and torch faster than you can say Morpheus.