Oh wow that is a good essay!
I very much like this idea about dilution:
a site aiming at a particular subset of users has to attract just those—and just as importantly, repel everyone else
I think we have managed that quite well on DC.
A couple weeks ago I tried displaying the names of users with the highest average comment scores in orange. That was a mistake. Suddenly a culture that had been more or less united was divided into haves and have-nots. I didn't realize how united the culture had been till I saw it divided. It was painful to watch.
I think this was mentioned by app103 before in another thread. It is a very important point, especially in contrast with the quote above about consciously repelling people: As a member of DC I don't want other members to be superior or inferior; we are all special in that we came here of our own free will hoping to achieve different things together. At the same time, I do not see DC as a place for everyone: we certainly are not a place to ask for software to be cracked for example.
I want my DC to keep being special, and I want my fellow users to keep being special individuals that have somehow managed to not ruin this place. In fact it has become "better".
So, while DC might not be as specialized as HN, we still managed to grow immensly and to "survive" that growth. Here's to my special place on the internet