Another variant that we came up with on holiday was to do with the politics and intrigue on the islands. We decided that the game was normally over too quickly when we end it just as the Aces are removed, so we changed it so that all the different islands had to have a Jack on it - that is, no further exchanges are possible.
This makes for a potentially much longer game, and makes the Jacks as ‘game enders’ that much more valuable. Trying to guess when the game is going to end is a big part of Card Pirates, so that attacks can be timed appropriately.
Thanks to an identical suggestion from someone else I now think that this should be an integral part of the normal game. I’ve therefore switched the rules around: playing until the Jacks are placed is now the standard rule, and the old Aces rules is now a “Simple politics” variant. See what you think!