Here's a third point: Seeing what questions get shared shows us what questions have the furthest reach. This ties in with Anonymous user feedback now in testingAnonymous user feedback now in testing. Imagine there's question that lots of people care about – we can take that data and
- could give incentives for keeping those far-reaching pages up-to-date,
- could see discrepancies between voting and actual "usefulness" of a question, draw conclusions from that, and improve the voting system,
- could look at what kind of questions are important to many people, what they have in common, and draw conclusions from that,
- et cetera.
This somewhat correlates with your point 1, since making it easy for people to share questions they consider useful also makes it more likely that they do.
Your point 2 is probably more important for the smaller sites; Stack Overflow itself certainly doesn't have to complain about a lack of page views.
Regarding configurability: It's well-known that we're very careful about user preferences. We don't want to become QuoraWe don't want to become Quora.
