I think you can get some of what you want by stretching the fourth as it stands, but not everything you'd want in a privacy amendment. But whatever you can get will be undermined by tech companies creating these anti privacy norms.

I can see two potential twists in your argument that people using tech companies create new social norms, which seems fairly reasoned on the face of it.

Firstly, there is a question akin to informed consent. People do use these services and voluntarily give up a lot of privacy, but is that an informed decision, or is it because they don't understand the significance of what they are doing? Although many people share much information with organisations like Facebook and Google, there have been significant popular backlashes against a number of changes they have made, particularly those that have resulted in information being disclosed to people that the users who supplied it didn't expect.

To extend your bathroom window analogy, there is an argument here akin to sharing certain normally private behaviour with your doctor. This is something you do by choice, in your own interests, and with a clear understanding that the information is sensitive and not to be disclosed to anyone else or used for any other purpose. This is fundamental to medical ethics, and in many places it is protected explicitly by law, so doctors can't be pressured to disclose that kind of sensitive information, even by the police. Lawyers themselves are of course familiar with a similar argument, again establishing attorney-client privilege or the equivalent as a matter of universal professional ethics and protected by force of law.

Secondly, modern technologies like computers and the Internet are part of a very young and fast-evolving industry that is changing our normal expectations in many aspects of life. In many contexts, the overall effect is positive, but there can be serious negative consequences in some cases. I think it would be unwise for the courts to attempt to reinterpret major constitutional or human rights laws based only on the fact that this week X out of Y people were happy to share something with a specific web site. It takes longer than that for social norms to develop, and as always the law should reflect our ethics rather than try to dictate how things should be.

I do think privacy is going to be a big issue over perhaps the next decade or so, as we collectively work through the implications of modern technologies and decide what is acceptable behaviour and what isn't. I also think you're right that dedicated laws are going to be needed, rather than merely trying to adapt laws written for a time before the kinds of implications we are now seeing and starting to understand. I wonder whether this won't be a generational issue, as digital natives who consider things like being on-line and having mobile devices to be basic and universal facilities start to assert their independence, while the political dinosaurs who clearly don't understand even the basics of how this technology works and its implications are replaced by the generation in between who are perhaps both more open-minded on these subjects and less willing to trust the government by default.