I agree that it helps those that are actively trying to look out for others, but to the typical brain dead driver I doubt it is of much benefit.
Will never forget sitting at a red light hearing a fire truck with sirens blaring coming up towards our intersection from the right side direction. The light turned green for our lanes and this guy starts blowing his horn at the guy in front of him. Well the guy in front of him obviously heard the sirens as well, and was waiting as the rest of us were, so the impatient horn blower pulls around the guy in front of him, zips out into the intersection right in front of the fire truck. Luckily for all involved the fire truck was taking a right, and had to slow down or he would have plowed that impatient idiot right in the passenger side.
People pull out in front of trains, 18 wheelers, etc, etc, etc, good luck with loud pipes, or hi-vis. Best to ride like you're invisible, because to many out on the road, you are.