Way back before bike helmets were invented I was riding on the sidewalk (I was a kid, and that's what we did) and hit a sprinkler head. Bike stopped, I didn't, and I sumersaulted over the handlebars onto the sidewalk. Gave myself a nice concussion with dizziness, headaches, nausea, the whole nine yards. I was probably riding about 10 mph. Do I wear a helmet now? You bet. Why in the world would I want to go through that again, with all the knowledge we have now about what repeated small concussions can do to a person. Of course, it is your decision, but you asked for outside opinions!