Are you 100% sure that you've valued yourself accurately?
I played "show me yours and I'll show you mine" with a coworker once and he discovered that we were both working the same position but he was paid $8K less than me. The difference was that I negotiated my salary like crazy and he didn't.
Information asymmetry is the best way for companies to ensure their employees are underpaid. While it could cause a bit of awkwardness between peers, at the end of the day I think it's better to know what others are making & let them know what I make, because it strengthens everyone's position.
If I negotiate for myself, I only need to persuade the company to spend $10,000.
A proven ability to keep your mouth shut could strengthen your negotiating position if you're using a quantifiable value-based approach.
I trust co-workers when they do what they say they will, when they are respectful & smart, when they show up on time, when they tell me when I screwed up in a nice way, etc. I could care less what they make--to me it would be a distraction.