Having done that kind of analysis twice for the same old computer (but for different disk) this fall, I can only concur.
A tool for which you could give a disk device and it would find all the syslog entries on that disk and order them correctly based on timestamps would be nice though. If they can provide that for "journald", then it might have some merit.
PS. you forgot from your list the fact that most this kind of binary formats take more space than text formats. When some program suddenly starts logging so much/fast data to your syslog that your disk fills, it's nice if the syslog format overhead itself is minimum, it gives you more time to act.
 Syslog notices only repeats of previous message, when something logs two different lines constantly (from same or different, but related processes), that feature doesn't help.