Is there any neccesity to upgrade from 3.0.99 to 4.x.x, for instance security reasons?
My NAS is running fine for what I do with it: sharing files with Windows PC, Mede8er mediaplayer and Mac Tablet, use of miniDLNA and backup to cloudservice with RSync.
So, for functionality I see no reason to upgrade.
Services running are:
Apple Filing
Downloader (X)
FTP (X)
MiniDLNA
UPS
SMB/CIFS
Sensors (X)
(X) means can do without