Agreed. I listened to an article recently about a study that purported to show that wearing a 'lab coat' increased performance. Similarly, I believe that the tDCS results could be explained by a form of mental 'priming'.
I would point out that line numbers are an option in VS. Secondly, I believe we are getting to a point where giant monolithic files should be the exception rather than the rule. Lastly, the ability to right click on a symbol and go directly to it's definition, see a clickable list of all its uses, and the fact that all warnings/errors are clickable means that the line numbers are less-important frankly. I still have mine on always but I rarely use them.