I understand why amateur restoration (such as putting tape over a tear or trimming an edge) can seriously decrease the value of a comic book, but given a choice of a damaged comic book or the same comic book with the damages repaired using professional restoration (such as leaf casting), I would prefer the latter.
That’s why I’m a little uncomfortable with the recent case of an unrestored Action Comics #1. (Of the around 100 copies of Action Comics #1 that still exist, only 37 have been certified by the Certified Guaranty Company (CGC) as unrestored.) The copy was graded 5.5 (from a scale of the lowest 0.5 to the highest 10.0), and was sold by Heritage Auctions last August 4, 2016 for $956,000. (The image below is an edited version of one from here.)
The price that was realized is a little high considering that it was estimated to sell for $750,000 and that an unrestored Action Comics #1 graded 9.0 was sold a few years ago for (only) $3,207,852.
But the thing that disturbs me is that this CGC 5.5 comic book was originally graded an apparent 7.5 when it was bought in the 1990s for $26,000. (The CGC uses the word “apparent” in its grading to indicate a restored copy.) Quoting from Heritage Auctions:
This copy was previously certified Apparent 7.5 by CGC, with tear seals being the only restoration noted. The tears at the top and bottom of the spine had been sealed using an archival quality glue, which bonded to the spine without degrading the integrity of the paper. The book was recently submitted to Classic Collectible Services (CCS), who were able to safely remove the glue, returning the book to its former state.
It thus seems that removing the glue resulted in the value being multiplied by almost 37 times.
This veneration of unrestored copies is also seen in the unrestored coverless 0.3 copy sold in the same auction for $65,725. (The image below is an edited version of one from here.) (CGC does not grade coverless comic books, so this one was certified by Comic Book Certification Service (CBCS).)
But it seems that CGC is making some effort to recognize the value of professional restoration. In 2014, it updated its restoration grading scale to differentiate restoration from conservation.