Ok, I think I'll get two 2Tb drives for the NAS and configure them as RAID 1 for some bonus redundancy.
Well, I finally got around to watching a film I recorded onto my PC called AI, after looking at the Digital TV card folder (from a old Hauppauge DEC 2000). Then I noticed the date it was recorded, 30th December 2004.

Is there really any point of having vast libraries of video and photos etc if you never really get around to watching them. I would just put all your critical data on a enterprise USB flash drive. Does you NAS enclosure have a USB port to backup to a portable drive?
Recordable DVD also is worthwhile as even many BluRay and DVD players will also display photos, music etc
WD Velociraptor HDD drives have MTBFs of around 1.4 million hours i.e. around 4-5 times that of other HDD drives and many SSDs will have MTBF of 1 million hours.