Niqab is Mustahabb
Abu Huraira reported that the Prophet said, "Allah said: My servant draws not near to Me with anything more loved by Me than the religious duties I have enjoined upon him, and My servant continues to draw near to Me with supererogatory works so that I shall love him"Our service of Allah SWT through our obedience of whatever He has commanded us draws us near to Him, and by doing more than has been commanded of us, we may draw nearer to Him still, inshallah.
found in Sahih Bukhari
Clearly, hijab is a command from Allah SWT and sisters draw near to Him through wearing hijab. And clearly, doing more than has been commanded is a way to draw still nearer to Allah SWT.
When a sister is already covering everything but her face and her hands, and she would like to do something extra to seek the love of Allah SWT, the only things left for her to cover are - her face and her hands!
Even if there were no other reason to wear niqab, surely this would be enough! How can it be "extreme" to wear niqab or gloves when her face and her hands are the only things the Muslim sister has uncovered in public to begin with??