I did just that too - kept my K1 as a backup reader to both my K2 and DX - I now realize that I can NEVER be without a functional ereader! And yes, I tend to keep my PD stuff on the K1 - b/c of the SD card storage. The rest of my library I can always download again from Amazon.
(Bring on the zombies & dead cats! - there's room for everybody!)