I think you were right on the spot. file command gave me this:

/my/dbfile.db: Berkeley DB 1.85 (Hash, version 2, native byte-order)
[download]

Then I proceeded to find a tool called db_dump185, which can dump contents of a BerkleyDB file prior to version 1.86 ( which is apparently when the db format changed )

lestrrat wonders why they couldn't just print out an error message like "Invalid file format" or some such thing....

So anyway... it looks like I need to db_dump/db_load and change all the files. That doesn't sound like a fun job, but I'm happy that I can at least read the damn things :-)

Thanks for your tip!