My .02 story -
When I bought a standalone DAC I needed a digital cable to connect my CD player. I went to a local shop that sold Nordost and Shunyata. They sent me home with a cost-effective cable from Nordost and also a Nordost Blue Heaven. They said, "Just try them and see whether you like one better."
You already probably know the story. Of course the Blue Heaven was noticeably better. Why? I have no idea.
Two years later I swapped the Nordost for a Cardas Clear. The Cardas was better. Everything just sounded more coherent. No single aspect of the audio spectrum was "louder", but everything sounded clearer, tones were more fully fleshed out. Wonderful.
Then, of course, I was able to try another cable. Jena Labs Valkyrie. Dang! It's even better than the Cardas!
So, in my experience, in my system, upgrading the SPDIF cable made a difference that contributed to my enjoyment. I appreciate that not everyone shares my views; I'm not trying to start an argument. Just wanted to share my experience.