I disagree with anyone who doesn't think sound cues are helpful. They're EXTREMELY helpful.

This also doesn't mean you need laser-sharp hearing, but if I were to err in any direction, it would be on more hearing rather than less. It's already a dangerous enough place to be on the road, and adding wind noise, I always feel exposed when I'm on a downhill at 30+ and the wind blocks out most of the hearing of rear-approaching vehicles until they're right up on you.

On climbs, you better believe that if I hear either the revvs of an 18-wheeler, or the whine of a motorcycle being ridden super aggressively (by someone likely not having a lot of time to see a cyclist on the turns), I'll ride ride off the road sholder into the grass in prepration for them to make sure I don't get flattened in the process. I definitely would not put anything in my ears that reduces hearing and that includes headphones.