Honestly wearing a helmet is about one of the highest ROI and lowest effort things to do. It's absolutely the smart move to wear a helmet.
The statistics tell the story, and your brain is the number 1 thing you should worry about protecting. Just look at the long term impacts that even light concussions have in a sport like Football. You can seriously screw your life up in something like a scooter accident when you go down hard head-first onto concrete.
1.) You dont get a lot of head hits in bicycle the way you get them in Football. 2.) The impact of helmets is smaller then people make it to be. 3.) You are making up cycling sound much more dangerous that it actually is, with or without helmet. 4.) And yes, helmets are annoyance. Helmet laws make people cycle less, that is fact too. Especially when it comes to trips to work, store or while running errands. If I have to look at least reasonable while dealing with bureaucracies and people, I can take bike but not helment (or need to comb hair and what not).
For #3, it's not that cycling is dangerous. It's that roads and car culture are dangerous. No activity exists in a vacuum.
And as for #1, the reason you wear a helmet is because the one time that you do fall headfirst onto concrete, the damage is life-long. It's not the frequency that you're protecting against, it's the inevitability of a fall and the potential lasting consequences.
And finally, I'd like to add that I'm speaking from a San Francisco point of view.
The statistics tell the story, and your brain is the number 1 thing you should worry about protecting. Just look at the long term impacts that even light concussions have in a sport like Football. You can seriously screw your life up in something like a scooter accident when you go down hard head-first onto concrete.