Really a warrant should be required to carry out any kind of in-depth, prolonged, or otherwise invasive surveillance or investigation into someone.

It’s not just which data or where they get it (though surely many types and sources of data should be restricted too, especially without a warrant) but the fact that they are building a profile, targeting, etc. at all. These are things the government/law enforcement should not be doing lightly or without supervision.

It's unreasonable to expect a person to understand when and where their data is being leaked/sold.

if the availability of commercial data becomes necessary for a functioning NSA, it will be used as an argument against any attempt to regulate data collection

I think it is reasonable for governmental agencies to have greater restrictions on their behavior without due process than a private company because the government has vastly greater opportunity to abuse this power.