How consistent to be National Master?

I don't think that blindfold chess will help most players improve their tactical ability and board vision. Blindfold chess is a different skill altogether. In my personal experience I find it to be the other way around. Pushing yourself to improve at regular OTB chess is a great way to improve your blindfold skills. All that energy you spend in a blindfold game trying to remember where all the pieces are does you no good in a regular game. That information is right in front of you, so in order to make the best use of your time, you have to utilize this information.

A side note on playing blindfold chess : it forces you to think in terms of lines of force or areas of control rather than piece position.

My experience playing blindfolded is that when I move a piece, I try to remember if any other piece (mine or my opponent's) controls the destination square (for safety check), and if I target some square (let's say my opponent's castle), I have to remember which pieces can target that square or move to be able to target that squares.

This way, you're bound to improve your piece coordination thinking. Well, that's my experience at least.

"but what I was really going for was that a lot of times you won't notice blunders, no matter how hard you look (until--usually--right after you take your hand off the piece)."

Yeah it is strange how if I do blunder, it's often right after the move when I notice. I don't know why that is, how I don't see a (usually simple) problem with a move sometimes until right after I make the move. It would be nice if I could get myself to think in the exact same mindset as if I already made my move, but I don't know how I could do that other than blunder checking. Even so, blunder checking still has saved me many times.

I call it the car-door syndrome.  Every time I've locked the keys in the car I notice just at that moment that the door has left my hand and is swinging shut and it's too late to do anything about it.  It's almost as though my subconsciousness is aware of it all along but for some reason conspires to keep me in the dark until the cruelest moment.

I see what you mean now.  I don't consider it a separate extra step, so I agree.

Well I still add a small extra layer of checking before I'm about to move or take my hand off the piece (even though my mind is, mostly, made up). It seems to help at least when I have some time, as it doesn't take long to do a final check.