I am also considering buying refurbished Kindle DX as the only other large format reader I can find on Amazon is Pocketbook 902 which seems to be about as dated and is more expensive.
The good thing about Kindle DX is that you can install Doukan distribution which will read just about everything including DJVUs (huge plus for me).
Also, from what I understand, you can install Doukan along with original OS, then you can dual boot of sorts depending on whether you want to read DRM books or not.
Even if you do not install Doukan, you can install other reading software besides the one that comes with Kindle.
About the only thing that is preventing me from buying Kindle is the lack of any external storage slot(SD or otherwise). With 3.3GB for internal user storage, it really should not matter though.