@towne32: No, that is not what I meant. The general vibe I was getting from the last comments was that it is OK to change special effects as long as only the 35mm sources are used to do it. Seems like I misunderstood your comment.
This is what he was referring to.
Thanks for that link. Seems like his approach has changed quite much in the meantime, I only knew his website. His comments in the video suggest that he might be correcting some things that were already present on the negative, but as long as these changes are only about dirt, flickering or poor registration, I can live with that. The result is certainly impressive.
I will now have a look at his other videos and hope that these will support my now more positive view on his work.