Although not applicable to DVD collections, I realized the following:
When I started using Dropbox, I uploaded some media files onto my account and realized that even for the most obscure items, someone out there has already done so before me. As a result, backing up those files was merely an exercise of data deduplication in most cases.
Exactly. Physical media is pretty much redundant in the case of things that are easily pirated. I still buy CDs and movies to support the artists I enjoy, but I've pirated albums and movies that I already own simply for the convenience of having a well done rip without the knowledge required to do so myself. (I've started making FLAC copies of albums as soon as I buy them now, but for older CDs that wind up scratched, pirating was generally easier and of better quality)