If you lack mens rea (only the absence of one of the two is needed to acquit) then that falls under insane automatism. Examples include crimes committed under delusional disorders, psychosis, or heavy involuntary intoxication. If you lack actus reus, less common, that is automatism. Examples include crimes committed while sleepwalking, experiencing a medical episode, or having a bodily reflex like sneezing.

There are numerous (some more infrequent than others) exceptions to the exclusionary rule. For example, the most notable must be inevitable discovery. Like the name suggests, police or officials acting with police (government officials or private security acting as an "instrument" to police directions) would have inevitably found the evidence being searched unlawfully. Take the 1984 Supreme Court case Nix v. Williams. Murderer of a 10 y/o girl was arrested and unlawfully questioned by police without his lawyer present, confessing the location of the victim. A massive coordinated search party of over 200 was grid searching the area and was only a few miles away from the confessed location of the body. The court ruled that because the search was already well underway and moving in the right direction, the body would have inevitably been found legally by the search teams shortly.

Definitely useful beyond just "knowing more." Mistake/ignorance of law is usually not recognized as a real legal defense to a crime if it simply involves "not knowing" the law. There are exceptions where certain circumstances might provide an affirmative defense, falling into the category of when an official legal entity misrepresents the law in a way that is reasonable to believe, in which the defendant wrongfully act in its direction. However, this may only represent official settings. For example, an off-duty police officer giving casual wrong/misleading advice is not the same.

However, in an inevitable sense, the highest of the judiciary branch, the supreme court, has substantial discretion (often hard to remedy against or challenge) over how the constitution is interpreted in real time.

has exceptions, including categorical exemptions that are are distinct and additions to exigent circumstances. different levels of protection for different types of private property. a home and its curtilage (basically its surrounding area) has the highest protections, but private property like commercial buildings / business locations still have strong protections.