isn't this rather obvious? doesn't everyone do this when it makes sense? obviously, it applies to other DBs, and you don't even need to store the file (just a single ssh from dumper to remote undumper).

if retaining the snapshot file is of value, great.

I'd be a tiny bit surprised if rsync could recognize diffs in the dump, but it's certainly possible, assuming the dumper is "stable" (probably is because its walking the tables as trees). the amount of change detected by rsync might actually be a useful thing to monitor.