I have an M1 license, I wear a DOT helmet, and I register my bikes. I also build all my bikes to be street legal with a 49cc engine, good brakes, headlight, tail light, brake light, and horn. Even though I've never been stopped by police, I figure it's only a matter of time as they get more common, for the police to start checking for registration. I put way to much work into each bike to risk getting it confiscated because of no license/registration. $18 is too cheap for me not to register it.
Also, having a headlight on during the day and having a brake light and real horn make my bikes much much safer to ride. I've seen drivers start to pull out in front of me and stop because they saw the headlight. I also give a little toot on my horn when I think someone might not see me as a safety measure. I take my life and health very seriously.