With the extensive wear, we decided to purchase a replacement post. Besides the obvious wear to the sisal, you can see how the post became discolored after years of use and abuse from little kitty paws.
Our cats took to the new post immediately, recognizing it is a special piece of furniture just for them.
On the old scratching post, you can see that the most wear is towards the top. My next project is to see if I can flip the base and the top on the old post and place it somewhere else in our house for twice the scratching fun for our boys.