I feel a personal obligation to meet with any YC company that wants to meet with me, the same way I would if a good friend asked me to meet with someone. I've taken enough from that network that I want to give back.
If someone cold-emails me, or has a mutual acquantance do an introduction, I usually don't feel as obliged.
But I'm not talking about cold-emailing -- I'm talking about personal relationships. They just aren't defined by having the same seed funder.
When I walk down the street in SOMA or the Mission, I too am likely to run into a developer that I know. And I'm not even a very social person. But I've been around the Valley & SF for almost six years now.
Maybe YC gets you off the ground faster, maybe you get that in year one. Still, I hope you are also reaching out to make connections with non-YCers.
If someone cold-emails me, or has a mutual acquantance do an introduction, I usually don't feel as obliged.