Re: How important is drawing for sculptors?
The author of Modelling and Sculpting the Human Figure, Edouard Lanteri, said that in his opinion drawing was more important for the sculptor than the painter. He was primarily a traditional/academic sculptor from the end of the 19th and beginning of the 20th century. This would make his statement seem dated, but his assertion is based on the idea that an artist that is dealing with form rather than shape alone must have a better working knowledge of the way objects are contructed. That dynamic hasn't changed and I would say that atleast in the figurative side of sculpting it is extremely important. One can look at the work of Michelangelo and see the benefits his mastery of drawing had for his sculptural efforts.
Perhaps the sculptor who works in forms that are more design oriented and less dependent upon realistic portrayals of nature could be excused from this exercise.
My own experience makes drawing indispensible for composition as well as sharpening rendering skills.