There's kind of an r/K selection thing going on, here. The people who do the least research per email have more time to send emails, so even if most link-requesters do their research, most link requests won't reflect that.
The people who write honest emails to me about how we can both provide value to each other do not happen very often but when they do I always listen. If fact if someone has a good resource that would provide value to my users I am happy to link to it. It's great to discover a "diamond in the rough" before my competitors to.
I am not advocating link spam here. I am saying that users should do their research and find sites that an inbound would prove value to both parties.