That's not quite correct. 91.3(b) allows deviation from any section of Part 91, not any rule in the book.
Hard to say without more details. However, the purpose of the declaration is not just to authorize deviation from the rules, but also to establish priority over non-emergency traffic. Without it being an emergency, the controller has no authority to move you up the priority ladder, but your declaration moves you very near to the top of the heap and gives the controller the authority to move other planes out of your way in order to get you on the ground as fast as possible.
Very possibly if I feel it's necessary to save the passenger's life,
but unless the traffic is Air Force 1, you shouldn't hear that after you declare an emergency.
That's not what the regs say. I think you should review 91.175 and the various ILS procedure options.
It's possible.
Regulatory relief isn't the only issue. Priority and additional assistance are the big issues, and the declaration gets you both from ATC. Otherwise, you stay in your place in the line (unless the controller is smarter than you are and, realizing the situation, declares an emergency for you).
Even if you're currently number 10 for arrival? You'll let the passenger die while you hold for nine other planes rather than declare an emergency in order to obtain priority?