@Skydog: What you describe should work, and I have done it with my Glo.
Does the new card show in the device information page of the settings? I expect it will as the card is seen by the PC when the Mini is connected.
When you insert the card, does the black processing screen get displayed? When an SD card is inserted, it is checked for changes against what the device thinks is there. The first step seems to check for missing or changed books. Then the black processing screen is displayed as it adds new books to the internal database. Both of these steps can take a while if there are a lot of books on the card.
With the copying of books from one card to another, I am not completely sure how the books will be seen. As long as you kept the names and paths the same, it should treat them as the same book. But, it is possible timestamps or something else change that would cause them to be treated as change books. And if the names or paths changed, then they will all be treated as new books.