Still, downloads are easily threatened by storage failure (internal/external)--literally in the blink of an eye, it can all vanish or become corrupted beyond repair and/or use. Of course if someone is thinking you can back up the downloads on a CD...then you would have been better off buying the box set anyway.
I'm thinking that I can back up downloads onto multiple machines in my house, as well as at least two places on the Internet, with relative ease. Whereas I can't back up the CDs without copying them to my computer first, and they can disappear just as quickly in the event of a robbery or house fire.
I think you have a greater chance of drive or online storage failure than a fire or robbery.To be honest, in the past decade, I've heard more complaints of data loss and/or corruption than house fires or robberies, so the odds that CD set being a poor investment drop to a considerable degree.
All of that aside, this is a one time investment with neverending benefits no matter what you end up doing with the data; its not like the old, expensive Time-Life music cd subscriptions for allegedly "complete" artist collections where one would easily spend hundreds on a few discs of material--most previously released and available just about anywhere.
The TOS set is a one of a kind--likely once in a lifetime release (the generations with a deep appreciation for TOS ages by the day, andd not many Gen Y youngsters care at all), so this could be as "Holy Grail" a media release as we will ever see.