Well, it would be nice if they implemented things to do when in there, for example:
Engine Room: Where you can speak to the Chief Mechanic and recharge the batteries whilst at surface (instead of telling the Chief Engineer in the Control Room) or check on fuel consumption
Ward Room: Where you can write in a fully editable patrol log, or read files and documents related to your submarine (manuals, specifications?)
Captains Cabin: Personal Diary? Listen to the grammophone, news broadcasts etc. What would be interesting, would be to introduce commander fatigue. Therefore, taking a rest in the cabin could regenerate stamina, otherwise, periscope accuracy and reaction times could be affected
Torpedo Room: It would be nice if they modelled this and let you view maintenance reports for your torpedoes or could schedule checks to be carried out. You could also have a look at the general health and morale of your crew, perhaps
Radio/Sonar: Apart from the obvious, it would be really cool if you could announce things to your crew and have it affect morale. For example "Contact Report Recieved" and then an option "Announce intent to attack"
I dont know much about American submarines though, but those are a few ideas.
