It is a good, concise article and I thoroughly agree with the points he makes.
I played guitar for about six years before I started playing uke. I have to say that it brought me out of a rut. I started learning more about theory and song construction.
It is always a good idea to learn a second instrument a it will teach you a great deal.
I teach ukulele and I always encourage my students to sing when they play. Some are a little shy at first, but end up finding it very rewarding.