BetterRed explained in the post #4 that the books originally never had any covers. Just all kinds of documents and such. I can understand the wish for reducing the clicks in Kindle, especially in case of short documents.
But I am interested in possibility to leave the cover (optionally) untouched while updating metadata.
Sometimes I choose smaller but different cover from Calibre 'download cover' selection, mostly to remind myself to go and trawl in the net for art. Or when covers in the selection have better quality, but boring artwork, I prefer to have a reminder that something else is available.