it's a rather old, thread, but I too still like the more versions-option.
Despite the workaround.
For example, if I have mybook - me.pdf and add mybook_lowres - me.pdf and I rename the author (say make it you) or the title, mybook_lowres - me.pdf will not be removed from my calibre-folder.
A post-processed file will often have a (significant) different size, so I will know which one I want to use if I use the edit-metadata screen.
Also, while I my library expands extreme, copies of my processed books take more space but more annoying, I have to use more covers (I want (small) covers for all books). This is a lot of slowdown during calibre start.