The expert who fitted me for my Keen boots told me that those particular boots had about 1700 to 2000 kilometers in them before they needed to be replaced.
Robert:
Just as an FYI, I wore Keen Targhee II mid-height boots on my first Camino last April-May. Before the camino, I walked perhaps 200 miles / 320 km in them while training at home. I would say I put about 1200 Km on them in total by the time I returned home.
When I got home, I noticed that the outer layer on the out-sole (bottom) had started to wear through on some of the lighter colored (grey) nubs. You could actually see the fiber material they used on the mid-sole. It was occurring more on one shoe than the other. But you could see that the lighter-grey material was softer and wore faster than the black bits of the outer sole. I am certain this was the design intention.
I sent photos to Keen footwear. They accepted this as a warranty claim, as I suggested to them that 500-600 miles was a tad short of what I thought I might expect for a pair of boots costing USD 140. Long story made short, they provided me an online voucher for a free pair of boots of the same cost and told me to keep the original pair.
I found a place locally that resoled hiking boots of all kinds. They resoled the original Keen boots using factory-supplied outsoles and returned them to me, with new insoles too, at a total cost (including postage) of USD 87. Just do a Google or Bing search for "resoling hiking boots."
Oh, this past week I ordered and received my free, new pair of Keen Targhee II boots under the warranty claim. I would have bought them sooner but they were out of my size - 13 US. I now wear both pair of boots for training but will use the pair that is most comfortable on my second Camino. I depart my home on 24 April.
So, I think you will find your Keen boots excellent for the Camino. I truly love mine. They are light, reasonably waterproof, have great toe protection and large toe boxes and I did not have one blister the entire 800 Km. I was just disappointed at the rate of wear. Should this happen to you, write them and include photos - I used my iPhone camera.
I hope this helps you or someone else.