This will not help you now, but I would check your Time Machine settings. The user library is backed up by default by Time Machine. There are several apps that I use that by default store everything inside their folder in the application support folder.
You mean it is my mistake? Could be, I started my rant based on posts in this forum, where it was stated that Library is not backed-up.
Since I have no way of checking it, I possibly should delete my my post. Because I do trust your statement.
I’ve never used the Migration Assistant before, so I cannot offer any assistance on how it should or should not be working. However, I have restored files in a Time Machine backup from one Mac to another Mac, so I know there may still be the option of recovering your old Global Inbox.
I just mounted my Time Capsule disk on my MacBook Pro and was able to navigate to a TM backup of a PowerBook on my network. I could just copy over the Global Inbox database and have everything restored to what it was with the last backup of the PowerBook. If you try this, I’d suggest renaming the old Inbox.dtBase2 to OldInbox.dtBase2 and open it like a regular database. In DEVONthink, copy the files from OldInbox.dtBase2 to your new Global Inbox and you are set. Let us know if this works.