I love Credence but really only because it's an Opeth song that's easy to play on the guitar, and the drums on it are noisy and...well just terrible, I guess I see where you're coming from.
The main difference for me from this list is that even though the "meh" instrumentals don't stand well on their own, I personally would rather sit through a "meh" 1 minute instrumental than listen to a "meh" 10 minute track like April Ethereal, In Mist She Was Standing, or Porcelain Heart when songs like When, Under the Weeping Moon, and Hessian Peel are just a click away. Not that I dislike any Opeth music, but, for example, For Absent Friends, if it's going to keep me from skipping to Masters Apprentices without being some masterpiece, well it better be short.