That's a bit.. cartoony? Doesn't look good all spikey.
I have some ideas and suggestions some to time consuming and ambitious though (and no doubt pointless).
More advanced ships. With rowboat remaining the basic
Pirate Shanty Competition, the best singer wins 100 bottles of rum.
Perhaps another map, more Carribeany without the big blue iceberg?
A record of a pirates crimes which can be viewed. Seeing who/when they murdered,ect. (Actually that seems pretty bad, I like the sort of word of mouth system that happens here)
At the risk of sounding to City RP like here.. what about a third faction which is civilians who will build/farm/whatever and give a goal for pirates to plunder and government to protect.. though it seems most pirates can do this and not take part in any crimes really so probably not the best idea.