I installed hella horns about a year after after I got my 2006 WRX. A woman in a van full of kids ran a stop sign and nearly took off the front of my car. I saw her coming and stopped in time. I was on the horn the whole time. As she rolled by, she never even looked at me. It was clear her Honda Odyssey was quiet enough to silence the weak factory horns.
I installed a set of hellas and have never had a problem with anyone hearing my horns now, including semi trucks. It's saved my ass a handful of times since then. Not bad for $55.
I consider it a safety item, and a cheap one at that.