People's arguments that you have an expectation of privacy are irrelevant: you have a genuine expectation of privacy in your home. If the state shows there's a compelling interest to enter your home (i.e. obtains a warrant), you can't stop them. Similarly, you can't stop them from decrypting your data. Well, you can, but you're going to suffer as a result.
Similarly, you don't have to show your hiding places. Suppose you had an encrypted folder structure and one of the folders was hidden to someone who doesn't understand how to see hidden folders. You don't have to say "there's a hidden folder", just like you don't have to say, "There's a false floor." Encryption isn't a 'hiding place': they've found the data.
Encryption is a locked door. The state wants to know what's behind it. Opening your front door to the police holding a warrant isn't self-incrimination (i.e. it in no way points to your guilt or innocence). Similarly, entering the password to your encrypted drive isn't self incrimination if the state has proved you're the sole possessor of the device.
Although the only way the password content can be incriminating is via the language of the password, the fact that a password works on a particular machine may be incriminating. This is the only line of argument that could work, for what it's worth, and none of these 'privacy' lines of argument. "Your honor, the state has no compelling basis for thinking my client had possession or knowledge of the drive in question. Compelling my client to enter a password on the chance it could unlock the files would prove that they did have possession or knowledge of the drive." &c. But once the state can show it's your encrypted data, it's game over. Fortunately, it's this "foregone conclusion" line of argument that the EFF actually pursues, and not the 'Privacy' line that seems to be popular in these replies.