The pirate captain story was originally considered by Ken Anderson while he was developing concepts for the Mansion. The Imagineers that finished and actually built the ride were inspired by some of Ken Anderson's concepts- but the Sea Captain story is NOT the story used in the Mansion.
The story for the Mansion is simple: You're touring a retirement home for ghosts. The first half of the ride, the ghosts are unable to materialize- they're frightful and angry. After the seance, they're able to materialize and you learn that they really have no interest in you.
The attic scene served as a sort of "gotcha" for the whole premise of the mansion. While most of the jokes you see are happy and socializing, the original attic scene was far more sinister.
When the mansion originally opened- the attic scene was far different from today. As you entered, you heard the famous heartbeat- with skulls popping out of hatboxes. As you worked your way in, on the left hand side (where the ghost piano player is now) there was a moldy corpse bride. The bride's intentions are left ambiguous- which further added to the suspense of the segment. Then, before you exited the attic, on the right hand side (where the bride figure stood for most of the Mansion's existence) there was a figure dressed in a tuxedo (the groom?)- who's head transferred to the hatbox and back. This clarifies the bride's intentions you had seen, and explained why there were skulls popping in and out of hatboxes.
Of course, this all changed soon after opening when the hatbox ghost was removed and the bride was relocated to his former place.
But the most important part? The scene could be interpreted different ways by the viewer. It was left to be interpreted by the guest, it wasn't a story hamfisted in via lousy dialogue and projections. And don't ask me how the hatbox ghost fits into the attic now.