I say yes to all lights.
I think a mirror is essential as long as it stays put... For instance I tried a helmet mounted mirror, and it kept getting knocked out of alignment, especially on rough road, it's pointless to have it if it points the wrong way and you have to keep adjusting it. A mirror you have to adjust every five minutes is probably more dangerous than no mirror at all... I wouldn't say it's essential all the time, only for the same reasons as in a car... Situational awareness... When you notice that giant wheel eating pothole coming up in your line of travel, you want to know there's a gap in traffic to swerve around it or if you have to brake to wait for one... When you need to prep for that left hand turn, you you want to know when there's a break in traffic to cross traffic from the shoulder to the center... And you need to do it without turning your head, because looking over your shoulder will cause you to drift the way you're looking, not to mention takes your eyes away from your line of travel, which might mean that you don't notice that pothole that your approaching, and won't know to steer around, because your watching behind (been there, done that: ripped the bars right out of my hand and put me on my back with my bike on top of me in the middle of a busy highway... Fortunately during a large gap in traffic)
As for looking cool, some people like to be fashionable for the coroner, but I personal prefer to avoid all coroners for as long as I can
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