exactly opposite - hdd data can be shredded easily, you never can be sure if wear levelling mechanisms allowed to actually delete some content on ssd
[...]
just use truecrypt with long password that you will remember
that time is about data in mlc chip itself, there is no way to be sure that usb stick will live longer than 5 years, especially if you have cold winter tin soldering can be gone after first year
there is no way to know if usb stick will survive more than year, there will be a problem with decrypting stenography and encrypted data unless you use exactly same software, burring things into the ground is no good until you put them like 2-3 meters under - as cold, floods and or construction can destroy them easily
instead i would have combination of mediums like pendrive, micro sd card, cd, dvd, blueray, printed copy, and sata disk
three - four sets in different location, perhaps at least one abroad
plus heavily encrypted failsafe backup stored online
most dangerous scenario is data loss and data leak, and i doubt that my backup needs to be interrogation safe