Toss me in the crowd that says you should wear a helmet.
As a kid, we rode all over the neighborhood and no one wore a helmet (not sure they had even been invented yet). Cycled the roads all over this hilly city for years as a teenager. Looking back, I consider myself lucky. Some where in the 20's I started wearing a helmet. Don't recall why. I know my mom was glad that I did... she might have even paid for it.
The day the helmet saved me was the day I was coasting down the gravel road from Peevine Falls in Oak Mountain State park. I was coasting at about 20mph when I started to brake to slow down a bit. Hit a bump and bounced one of my hands off the handle bar (if I hadn't been trying to brake with those old style canteliver brakes, I wouldn't have crashed). I went flying off the bike and somehow turned and landed on a combination of the shoulder (broke my collar bone) and helmet.
The helmet had MAJOR structural damage, and there was a nice gouge in the sell from the sharp edge of a piece of gravel that would have ripped my scale open (at the very least) if it wasn't for the helmet. The helmet did its job well enough that I never lost conciousness, nor had any symptoms of a concusion.
While not as important as a helmet, I also don't ride without gloves. I've experienced the pain of tearing up my palms from even a minor wipeout. But more frequently, I've experienced the protection of my palms because I now ALWAYS wear gloves.
After all, if you are taking a spill from a bike, you're most likely to either stick out your hands to catch yourself (so you need the gloves) or if you can't get your hands out in time, your likely going to hit your head.
Of course I can't force anyone else to ride with helmet and gloves... well, no one besides my kids.