I just like e-readers.
My first Kindle was the K2. When I purchased the K3, aka Kindle Keyboard, I offered my K2 to family and friends and nobody wanted it, they like to read “real” books they all said. So I kept my K2 and made it my bedroom e-reader and took the K3 everywhere I went.
Since then I kept the at home/ portable pairing and older models serve as backups if a battery is drained. At this point I have so many Kindles that I have thought about putting specific subjects or genres on each Kindle but haven’t done that yet (this Kindle for mysteries, this Kindle for Sci-Fi, etc).
By my count I have had fourteen different Kindle models. I purchase new models to get a better screen, lighter weight and / or faster E ink response. I’ve kept most of my Kindles and the few that I traded in or sold I have regretted parting with for one reason or another. Like I said, I just like e-readers.
That said, if you are happy with one e-reader I don’t think you are missing out because you don’t have multiples.