A mirrored pair of disks like this is only going to help you in the event of a disk failure. Effectively both disks are written to simultaenously, with identical data. So if the disk controller fails, or more likely, you delete a file by mistake or your computer gets infected with a virus your RAID won't help you.
Mirroring will increase your reliability, but to overcome issues such as those above you'll need a back regime (to cope with a hardware failure) which includes archiving rather than just taking a snapshot (in case something bad happens and gets backed up over your snapshot before you realise it).
Big disks are cheap and if your data is that valuable you'll not mine spending a few quid on them. If we're talking documents, spreadsheets etc. (and not PPRuNe databases) then you're probably look at a few tens of megabytes, in which case you'll get plenty of old versions on an external 500Gb USB2 or Firewire disk.