Some very good points here, but overall, it seems that your idea for the Ocean (which I like) would be a neat POD. Or a bigger expansion, somehow. Maybe a large 'thicker' paper underlay sheet (so not a board) which encompasses the entire board, leaving a circle around it, as the route around. The spaces between boards ('boardlet' areas) could be those pirate coves or safe harbours (one on each side).
other than that, I like a Maelstrom deck (want a card that takes you to Davey Jones' Locker, *and* a portal/whirlpool to the CoC, of course)