Lyle:
My own method is to bring along a sleeping bag rated 10*F warmer than my worst expected environmental temperature; the bag being my last refuge, the place where I can do that most important thing–stay warm and dry. Like you, I view clothing as supplemental for sleeping, to be used only in an emergency. This is the older, tried and true method.
My point is, that many people today talk about taking a sleeping bag that that isn’t rated warm enough for expected temperatures, and wearing all their clothing to bed to make up for the deficit. As you say, this leaves no margin for error; or, no margin for safety when the unexpected occurs.
But, perhaps its all talk, as no one has written in to endorse the method (Matt’s statement is not that strong).
My inquiries, to the people who DO rely on their insulated clothing to supplement a deficient sleeping bag, are as follows:
(1) Whether they find wearing the fiberfill or down clothing warmer when wearing it inside their sleeping bags, or using it as an inner blanket; and
(2) Given that wearing the fiberfill or down clothing during sleep breaks down the fibers and down more quickly, thus reducing the warmth of the clothing and requiring replacement of it sooner than usual, whether they view the reduced efficiency and increased cost due to more frequent relacement, as a fair trade off, as part of doing business.
Conan
Conan