I have been keeping doubles of hardware since the 90's and now that things are starting to fail, I am glad. I have had a 2600, Colecovision, Dreamcast, TG16 (hucard port), TGCD, Intellivision, X360, Jaguar, Nuon, Atari 7800, PS all die on me in the last 10 years or so. All needed (or need) repair, I had a backup for all except the Nuon and the TGCD - and I don't give a crap about one of those two...
As far as games go - no, I don't need multiples unless they are on a different console. Games are not like records, where you may find huge differences in quality of the pressings. I have several copies of some of my favourite records as I find better sounding copies...
I used to "collect" Atari 2600 games so I may still have a few dupes (Sears/Atari releases), but I don't think I have any other dupes that aren't in a trade pile..