The way Raven's Cove is laid out right now the central part of the main island is right around Crazy Ned. I could see barricades built up from the broken dock and down by the beach where the mine tracks start. The problem would be the wharf by the Fisherman's cabin. It's a little too close and I could also see the skeletons struggling a bit with that ramp.
As far as any benefits from Invasions, I look at them more as social gatherings. Pirates chat each other up before hand, crew together and help each other out. They also make good guild outings and even recruitment opportunities. While a mastered pirate won't much if anything, aiding guildmates and friends is fine with me.
Long term solution might be if Jolly himself drops a chest or something to reward participants when he's beaten. Doesn't have be the most primo reward, but might be motivator.