[Dovecot] Migrating from UW: mbx detection and conversion

I want to migrate my big mail folder hierarchy in preparation for converting from UW-IMAP to Dovecot. I've got a bunch of mbx format folders but some remain mbox. Has anyone done this? Any scripts out there for automating the conversion to all-mbox?

I believe the only format conversion available is mailutil (part of UW-IMAP) and it works by opening an IMAP connection to the server and moving messages from one folder to the other. Is there any simpler method?