Thank you for your kind words! I am glad and honored you found the article of interest!
A FileVault sparseimage is basically a disk image that you can mount on any old Mac with Disk Utility. In that light, a copy of a sparseimage constitutes a reliable encrypted backup. A drive failure on an encrypted Home Folder would probably leave the virtual volume that is the "Vault" in an unstable, unusable state, making keeping good backups of any encrypted files extremely important.
The only drawback to backing up the encrypted images is that they are susceptible to corruption, a phenomenon which can sometimes lead encrypted volumes to stop mounting, with no apparent cause or reason. Unencrypted data is obviously a lot less fragile to such problems. The decision is, in the end, yours and will depend on how much protection your data needs from indiscreet eyes.
I hope this helps,