Come on Gary I have the same weather you have the very same weather and vally here last 20-25 years. You would know this if you would walk the roof:p
We have the same valley cut on our roofs as well. They last as long as the main roof so I don’t see the issue. Metal valleys are crap. Ice daming occurs in these all the time.
Gary I agree somewhat. You might be able to see a portion of it but no way all of the damage and how do you get pics like Charlie did from the ground? Also I wouldn’t of wrote up the valleys either unless something was obvious. In Oklahoma there really is no such thing as estimated life expectancy. The weather there can tear up anything in a moments notice. If I was inspecting there and someone asked me how long the roof might last I would tell them until the next big tornadoe or hail storm so make sure your insurance is current ;).
No problem with valleys here and conditions of severe winter can’t be much worse than here.
Composition valleys get replaced at the same time as the rest of the roof. 
Depends upon sun angle. Ice/snow can sit in these valleys and freeze/thaw over weeks, and loosen granules. Rain here can wash-out shingles in a hurry, especially if there is a large roof area causing heavy water run-off down the valleys into gutters; somewhat like a funnel. Depends also with the quality of shingles.
I have replaced alot of these deteriorated valleys back in the 70’s when I roofed homes.
No two home inspection reports can be alike. I really believe that now.
Nor two inspectors;-)