Gotta add my 2 cents to this:
You use many real world examples to try and justify what you are trying to protect. But changing your IP is not really the same thing as closing the bathroom stall door as you put it. It more like just moving over to the next stall.
Closing the blinds, closing the door, closing your windows, locking your car. All firewall similes. Going out and moving your car a couple of spots over, that would be changing your IP.
Leaving your purse in the shopping cart. vs Leaving your purse in the shopping cart in one aisle over. Same end effect as changing your IP. The person that wants the purse only has to walk one more aisle over. Don't know about you, but that doesn't take much effort if I want that purse.
Now locking your doors and rolling up your windows (firewall) vs locking your doors and rolling up your windows and moving your car over a couple of spots in the same parking lot (firewall and changing IP) added nothing for security. It just means the person looking just had to move over a couple of spots. Not only is this useless but it doesn't take real amount of time. Once again, walking that extra little bit if I want your car or its contents isn't going to do anything.
Also, you grabbed another posters information earlier to show the ease to retrieve informaiton. Question is, was this information that the poster had freely posted before? I find it safe to assume that if I were to post it, then people are going to know about it. If I don't want people to know it, I don't post it. So really, to say you've discovered something about a person when the person sat there and told a large group of people isn't much of an acomplishment.
Since I am posting from a static address, people are going to be able to tell where I work. Good for them. Here I'll make it easy: I work for a company called PAMI. Now people know and will be able to look it up for a long time to come. Does it matter? Of course not. Had it mattered I wouldn't have posted it. So if you do not people knowing were you work or such information, don't post it.