human-memorable password makes it safer, attacker has to hack you *and* need
physical access to your backups.
That being said, encryption is also pretty secure against yourself if you forget your password. Which tends to happen more often with passwords that are not used on a regular base (exactly like this scenario of a offline use).
It might also be a good idea to have a copy in different location, not just at home. One physical location is a single point of failure.
Just for fun I carved a private key into a bar of gold and put it in the firesafe. Then I've written a small procedure to graph their relative value over time, and I update it every morning.
It will be interesting to see which part is more valuable in the end...