Balsa does support attachments. When I click on a jpg in Balsa it immediately displays the image for me in the preview pane. Any other quick graphic viewer will do. Easy as pie. In the process of autodetecting your mailboxes Balsa will recurse into the subdirectory and put the mailboxes in their own subdirectory.
Balsa can read many mailbox formats natively.
Thanks to Jesse D. Sightler for putting this page together.