I have to agree with KM about on the highway. Your sound is coming out of the back of the bike, most of your problems are ahead of you. I won't stay alongside a car unless I make eye contact with the driver or they catch up with me from behind. I don't stay near vehicles with dark tinted windows. Loud pipes are no substitute for a cautious rider. KM is also right that motorcycle awareness has been a larger public concern in recent years. Motorcycle safety has also become a larger public concern. Teaching riders to use the left 1/3 of the lane when possible, for example, helps make them much more visible to the cages, since the bike appears in two mirrors.
With that said, I think that bike volume might have a slight benefit at intersections, where a large number of accidents occur. At slower speeds or stopped positions, your sound keeps up with you. If you have a vehicle behind you, some of your sound is bounced back forward into the intersection. Bikes are commonly cut off either in left turns or by a car turning left, and in these situations the bike's sound might actually make it across the intersection. Nevertheless, intersections tend to be around houses (do you want your neighbors to hate you?), buildings (your favorite diner or coffee shop), people, etc., where loud pipes can be most obnoxious. Distracted drivers are also distracted from environmental noises!
Loud pipes also drown out other hazards, like emergency vehicle sirens. If I can hear a bike but can't see it, it bugs even me out. Loud bike driving over an overpass as I go under it... sounds like a bike is swerving across the road somewhere. They cause unnecessary panic, spook dogs and horses, wake me up at 1 or 2 in the morning, usually with extra revs thrown in, rattle windows, and are counter-productive in the continual struggle to make bikes more recognized and respected. I even heard a loud bike drown out fog horns on the bay one day... the boats use those sounds to avoid hitting each other.
Like with my guitar, I prefer tone to volume. The Vulcan has decent volume and a nice tone. With stock exhaust the noise limit 83 decibels at 4125 rpm (there is a sticker with this info on your frame). Try standing behind your bike at idle one day while somebody holds it at four grand. It's always louder when you're off the bike.