We paid the extra money to visit the sub, destroyer, and the Endeavor. It was stiff but worth it, especially on the replica of the Endeavor. It has, itself, been sailed around the world so its fittings genuinely suggest the nature of Cook's trips aboard it. You'll be amazed at what the crew put up with! (And not that greatly improved 300 years later, if the destroyer is a hint.) The volunteers must be commended, too. They are all very well informed and enthusiastic. If you're interested, they're delighted to tell you everything. As for the museum proper, you can skip it although, at $7, it's one of the more reasonable attractions in Sydney.