The difference between your friends guitar story and most of HNs computer usage is that your friend was just trying to learn guitar while most HNers use a computer as a job. I think you would agree that someone whose job it is to play guitar should probably spend (money doesn't equal quality, but just using it as a point) whatever they think is necessary to have the best guitar for them.

When it comes to using a computer all day, every day, having great (not just okay) input devices, and great (not just okay) monitors not only can make you more productive, but also save your eyes and prevent RSI. Desks also fall into this category of saving your actual health.