In my 6000 miles of always taking the lane commuting, I notice riding in medium traffic is safer than low traffic. In low traffic, you get the prankster types. People see an isolated cyclist and think it is a great opportunity to do something dangerous with no witnesses. In medium traffic, one is far less likely to be bothered by this type since there are so many others around to take away their anonymity.
What do other's observe? Sure, you will get more honks in medium traffic, but Ill take a million honks over one person who tries to throw something at me or intentionally run me off the road.