Is it worth updating the firmware from 3.24 to the latest nsa220 plus firmware or is there little added benefit?
Who will say? From the release notes:
Modification in V3.25(AFG.0)C0 | 12/2011
Allow Media Server support to choose generating thumbnail or not
Media Server: support id3 tag by libiconv
Online firmware upgrade stopped unexpectedly
Fix some problems of power schedule
Solve smbd failure while sending large files to FAT32 formatted USB device.
Fix HDD wake-up problem
Sansom claimed that 3.25 supports >2TiB disks, but that's not in the release notes.