There are a few threads going on here but the main one seems to be: Should we care about "privacy" of information available in public, and if so, how do we set rules (Given that it's in public)?
I think the answer to the first question is undoubtedly yes because of the way technology is advancing. Yes, we've always been able to see people in public, but we've never been able to do it in a rapid automated fashion on a mass scale, or catalog and query natiowide databases. This creates new implications for privacy. In the past the government simply didn't have the resources to know exactly what religious ceremonies, political meetings, protests every American was going to. Now they do.
This may mean an expansion of 4th Amendment protections (@sharemywin mentioned the idea of a new amendment, but I think this is exactly what the 4th Amendment is for). In Jones the Supreme Court said you can't attach GPS devices to cars without a warrant, and 5 Justices said we may need this type of protection for location data generally. Since then many lower courts have applied this protection to location data generated from cell phones (even public locations), which I think is correct.
As far as setting a standard, I think the best approach is to require 4th Amendment protections for location data generated from an electronic source/device. This is what a number of states have been doing to address demands for cell phone location data and police use of stringrays. It also directly goes to the issue that electronic devices are given government unprecedented power to record, store, and query our location data, which makes that data more sensitive and suseptible to abuse.