[barbazfoo12]

Right. But if you only ever write and rarely ever read your writing will not be as good. Reading is essential to good writing. The quote you use is encouraging the reader to write, but it also presupposes that the reader is well read ("A lumberhouse of books in every head"). Maybe that's not a coincindence.

Is there a difference in encouraging a "scholiast wit" to write versus encouraging a "dimwitted blogger"?

[CeiII]

Yes, I agree. Like all things it's a balance. In looking to refine skills everyone will require tuning in different areas. A programmer may be great at writing code but often fails to identify re-use of libraries/patterns. Reading others' code and technical articles may assist him/her in developing in that area. Likewise you may be able to tell when a writer lacks a 'lumberhouse of books'.

Being aware of why you are not developing a skill is probably key -- review from others helps to provide insight into potential underdeveloped areas.