I still have a PRS-500 but after a replacement battery died I gave up

and moved to a T3S

.
I never cared much if lrf was not available as long as epub or mobi was available but calibred epubs or mobi to lrf.
A bigger annoyance was that I couldn't access the internal memory of the 500 anymore from a PC from Windows 7 on. Not even with Calibre. No drivers available for Windows 7 without the firmware upgrade. I'm not sure, however, if the upgrade fixed this problem. I fixed it with XP in a VirtualBox on a Windows 7 host. Another option was to ignore internal memory and use SD-cards.
Happy New Year,
hansl