OS X V10.7 Lion :: Mac Mail - Can't Restore 'On My Mac' Folders

I could not find any direct reference to my question - believe me I searched everywhere before coming here. 

Some details:

- OS X 10.7.4
- Mail 5.2 (1278) 

Prior to my intervention, Mail was not really running at all; It was making entire system run slow and I could not send mail at all. I decided to backup my Mail folder and Export all the 'On My Mac' folders before making any changes. 

After all was backed up, I rm -rf ~/Library/Mail ; I then reopened my Mail app. I re-added the old account. All my online stuff is fine obviously as it is delivered through IMAP. The 'On My Mac' stuff however is seemingly a different story. I attempted to import the exported 'On My Mac' folders, however after they were reimported, none of the subfolders were there, and 1 mailbox in particular did not report an import failure, but does not even import into the 'On My Mac' section. 

I also attempted moving the old Mailbox .mbox package/folders to the same place they had been, but this does not seem to work either. I am just presented with an empty folder structure upon reopening Mac Mail. 

Info:
Mac OS X (10.7.4), Mail 5.2 (1278)