It definitely is a variation of that belief. Could you elaborate on why it is mistaken?
I think:
1. Whether something is valuable can only be discovered if you try to set a price and sell it. Until then, you can not know.
2. LinkedIn has big part of it's business selling 'InMail' at around 2$ per piece. So clearly some people's attention is so important that strangers do pay money to send them mail.