I would make a distinction between 1) working on some project ignoring what others are working on or what they would say about the potential value of the work until you have reached some milestone and are ready to present it to the world and receive critical feedback, and 2) working on something without concern for anyone else ever finding value in it.

Feynman is clearly saying disregard others while you are doing the work, not disregard others when you present it for feedback and criticism. That is the spirit with which I responded.

As a developer, there is a third option where your work is simply ignored. If it is functional for you and you are satisfied with your own work, then sure, feel free to disregard others lack of interest, like an artist who values their own work but meets a deafening silence. But please don't disregard serious criticism.