Well that "restore" should work but it's not quite the same as backing up the whole library.
It is too much? Well, I come close to that but - like you - I have a local back up and two remotes (on in my car, one stored at a relatives house. So for the online storage, rather than backing up the entire thing again, instead I just backed up the photos themselves. There are many options: Flickr, Picasa, SmugMug etc. However, check the terms of your account carefully. While most sites have free uploading, you will often find that these uploads are limited in terms of the file size or the bandwidth you can use per month. For access that allows you to upload full size pics with no restrictions you may need to pay.
FWIW I use SmugMug. My logic is...if the Mac fails, I have the local back up, if that's gone I have two more, and then if they're gone, well at least I have the photos. Plus I can view them from any computer in the world.
Regards
TD