I feel like there could be a bit more spice to the PG metagame, something for the larger players to be beating the hell out of each other for, and for smaller players to be striving for as they grow. I say that it would be a good idea to introduce artifacts.
Unlike voodoo cards their effects would be permanent, such as +1 gold from every trade good sold and such, or a small attack boost. But each one would be unique, no stacked abilities, each one would be the only one of its kind. There would also be a permanent list of the current owners of each one, and which of their fleets it is assigned to (But not the port their in).
They would have multiple ways of being passed along, firstly, you can randomly find one by raiding NPC's, or something of the like, or a chance by raiding a player's fleet that has one assigned to it. Next you HAVE to assign it to one of your fleets, so that it may be passed along and can always be within reach of other players (this fleet would also be incapable of having the last ship removed just like danger rating). After that, you can loose it in two ways, by either having somebody successfully raid your fleet (there wouldn't be a 100% chance of artifact loss unless you are out of money) Or you leave the game long enough to have your trade routs quit, whereupon the artifact is cast into the sea, to be found anew.
Just an idea.