As someone looking to potentially merge ArchivesSpace databases in the future, I would like a way to export out the database to include events, accessions, and other records that don't currently export from ArchivesSpace. This would be helpful for migrating to and from a hosted instance or merging databases (like importing a repository onto an existing ArchivesSpace instance with other repositories). [post edited to remove suggestion that this could help with backups, which is already addressed with MySQL, thanks and !]
I do like the idea of being about to smoosh together two ArchivesSpace sites easily and completely. I know there's the HM tool that comes close, but having a plugin or tool to easily combine two existing sites into one would be super useful. Though it's likely most people would only do it once, I would think there's more than a few people who would want to do that.
I think this would be more of a smoosh/migrate/combine thing, and less of a backup thing, since just using mysqldump for the backups is probably fine. I'm thinking something almost like the tools to migrate out of AT & Archon, but for going from ArchivesSpace to ArchivesSpace.
For catastrophic failures, regular MySQL backups are probably the way to go.
For merging ASpaces, this tool from HM can be very handy. I think that adopting and extending it to support the things it currently doesn't (like locations) would be very useful, particularly if the transfer of resources between repositories was made more robust.