This is a good question, we're trying to plan something in my region, thats low profile yet very similar.
The Ultimate for me would be a Mariner's BBQ, where it's celebratory festival an Ode to the Pirates of Old. Except in modern barbecue format. (The clean up is easier that way imo especially if held in a park) People dressed up as the pyrate like, or your favorite famous pyrate character. Theme would surround the "Nautical", surrounded by the comforts of food, grog, story telling, and just ultimate revelry in general.
Of course there would have to be the music, lots of Flogging Molly, The Corsairs, Whirly Jig Monstrels, Iris & Rose, Running Wild, Grave Digger, and other great Pyrate metal bands. (Me is a huge fan of Pyrate Metal!)
That'd be the ultimate pirate gathering for me, hopefully one day it will be pulled off most likely on a smaller scale
Pax,
Cyanne