Again, I am not advocating one side or the other.
As stated, you must realize the specifics of the situation.
I know I am opening a can of pit vipers here, but personal experience has put the awareness of my presence with cagers when I throttled the Harley and my "loud pipes" were taken notice of.
I am not advocating the loud pipe thing either.
I look at this more pragmatically.
The high viz. stuff creates a condition of standing out, just as much as alot of noise causes people to garnish their attention to the situation.
Experienced drivers fall into two separate conditions and no one driver stays in only one.
The first is that the visual becomes so ordinary that they start to ignore it.
Secondly: Same with the sound of loud pipes. I have personally witnessed this as well, when the loud sound meant nothing because the drivers were so use to it. it meant nothing but background noise.
These experienced drivers also over time learn to watch out for the bikes in large part but some miss and accidents happen. So it becomes sort of a net zero sum gain.
On the other side of this are the inexperienced drivers who become startled and/or are not use to seeing high viz so they pay attention to that. This sometimes startels them and causes accedents, other times they pay attention and deal with it.
Honestly, there is no one formula and you will never know what if anything has saved your life.
Most of this IMO falls to the training and practice that should IMO be mandatory for all drivers.
But that's another discussion.