Don't get me wrong - the mechanical reasons you list for the difficulties they face are en pointe. I dispute none of them. And I don't think that "hey guise be nice" is likely to accomplish much. There needs to be a concerted effort from the top down to turn Reddit back into a community - a large one, that respects a great diversity of opinions and interests - but with a set of "core values" that they can defend. In terms of corporate hucksterism, they need "guiding principles." They used to have them - Alexis and Steve salted Reddit heavily with the articles they wanted, created hundreds of shill accounts and sock puppeted their way to a community they wanted (the early and heavy love affair for Ron Paul explained in a nutshell). But ever since, the "guiding principles" or "core values" of Reddit have been "traffic at any cost." 4chan, at its mightiest, had more traffic than Reddit. And it was still run at a loss out of Moot's basement. Traffic only goes so far. At some point you need to point to the kind of traffic you've got. I stopped having that conversation back in '09 - there were plenty of people who were interested in Reddit's numbers until they saw what was driving them (80% porn search). They could do it if they wanted to. But they just don't want to. And it makes me sad.
I started using reddit when it was still written in lisp, I think because of a comp.lang.lisp post about it. I remember those days too, though I was never really part of the community there. The posts they were making were mostly stuff that were circulating in techie circles, or from sites that were popular in them, and the "core values" were those that were common among hackers before the word got appropriated to mean "startup kid". Not coincidentally, most of their early users were techies too. They didn't have to create a community, they imported one that already existed and which they were already a part of. Alexis and Steve's sockpuppeting just made it an attractive place to migrate to at a time when the old watering holes were in decline.