In your opinion.
I am not arguing against using sanitizers, nor am I arguing against a quick visual check, there's nothing wrong with it if it's convenient. It's a pretty good idea really.
I am arguing with the notion that a visual check is a "best practice" from a sanitation point of view. It is YOUR practice, but perhaps not BEST practice. It doesn't gain you anything more than a warm fuzzy feeling that you're doing a good job.
I'm perfectly content to take the spray nozzle from my hose, blast out the valve in a circular motion with high pressure water, then spray it thoroughly with Star San. I am willing to trust that this practice works the same as yours, even if I do the whole thing with my eyes closed. Again, this is not about a practice, it's about a feeling.
I'm really not trying to be combative or start an argument (any more than I already have) and I'm sorry for that. I hope you read this in a neutral and calm tone, as that is how it is intended. I just want to make sure we are being clear that you are one brewer sharing YOUR practices that work for YOU, but that doesn't mean they are accepted as BEST practices necessarily.
There are other ways to accomplish the same goal that can provide a warm fuzzy to others, like copious amounts of high pressure water in leu of being able to see into the valve or you could (as Eric has suggested above), fill a capped elbow with PBW solution and hook it up to the valve for a couple hours, then spray it out, then sanitize (I might actually start doing that)