I think the change was made for a good reason. The point is that the new storyline is that Barbossa and his crew are after Jack... AND THE TREASURE.
So this drunk pirate is sitting there with the treasure map in his lap... I think it's a humorous move to put Jack in the barrel looking over the guy's shoulder to read the map so he can beat them to the treasure. If Barbossa has a treasure map and is racing Jack to get there, Jack would somehow have to acquire that information as well. With limited time and space to do so within the confines of the ride, this seems to me to be an ingenious way to do so. It's not an hour and a half movie... It's a fairly short dark ride.
The little girl was a fairly static character in my mind... Not as important as the redhead, or even the dunking mayor's wife. I think of her more like the women that are chasing/being chased. I could take them or leave them, especially if they were replaced with something more impressive.