I was at one time a compulsive data hoarder. I collected huge numbers of files of music that I never listen to, videos that I never watch, audio and print books I never enjoy to and software programs that I would never install or run. I cannot even blame the huge collection on sex. There is absolutely no porn in the entire collection. There is instruction on some obscure programming languages that I have no intention of ever learning.
I have the same issue, but primarily just with ebooks and comics. At the rate which I manage to read them now, there is no possibility of me actually finishing the collection I have within an average lifestyle, but I still keep acquiring more.
As you say, this is not a space concern, since a few external hard drives take up very little physical space; unlike the ever growing pile of dead tree books. When I sit and think about it, though, the time I spend gathering and filing the collection could be much more productively spent reading more of what I already have.
I do wonder if this behaviour is a modern manifestation of something that made sense for a stone age hunter gatherer.