If you store the data encrypted and something happens to you, the files are worthless to someone else, maybe a family member, who might enjoy/benefit from their availability. Have you put the encryption key in your will / living will, or already given it to people close to you so they will be able to access your stuff when you're gone or incapacitated? Or are the files only for your own eyes?
That's a very good point. I am currently young and arrogant so I have yet to create a will. There is a 'live' copy of my shared data which is accessible to the appropriate people, but they would be unable to access my backups. That means disasters that strike both myself and my live storage location are still a threat to that data.
I think having multiple encryption volumes on the drives might be the answer here. Potentially a 'personal' volume which only I know the key to, and a 'shared' volume which I share the key across will / lawyer / loved ones. To make that more useful, storing a clear-text list of who should know the shared key with the data seems like a reasonable precaution.
I think the next time I rotate through my archives I will implement that type of multi-volume solution.