One interesting thing about the letter is that Joseph Smith himself copied it into the Letterbook; i.e., this is in Joseph's own handwriting. In the Joseph Smith Papers, material written in Joseph's own handwriting is put in bold text.
I think it's important for those who consider Letter VII to better understand Oliver Cowdery and what motivated him. These letters give a good feel for what he was trying to do as a follower of Christ.
To me, they help demonstrate that the last thing he would have done in writing Letter VII would be to deceive or confuse the Saints.
I find it interesting here that Oliver has already become a printer. He writes, "it may look rather strange to you to find that I have so soon become a printer and you may cast in your mind what I shall become next but be assured my changing business has not in any degree I trust taken my mind from meditating upon my mission which I have been called to fulfill." Of course, Oliver would go on to print not just the Book of Mormon, but newspapers and the Book of Commandments.
Joseph also copied a letter that Oliver wrote to Hyrum:
Obviously it's interesting that this letter quotes from D&C 18, which was given at Fayette in June.
Then there is an earlier letter from Oliver to Joseph, again copied by Joseph Smith himself:
Next is a letter to Oliver from Joseph, copied by Frederick G. Williams:
— Oct. 22d— 1829