On the biological side, is there any evidence that we have reached an equilibrium? (I'm asking genuinely)
I'd say the negative correlation between education and fertility has been established pretty firmly. As a simple demonstration: if you sort the information here by fertility rate in descending order, you'll find that the countries with <2 children per woman are mostly first-world countries. There are more than a few countries in Europe, for instance, where immigration is the only thing keeping the population growth positive, and let's not even get started on Japan. And it goes deeper than country-to-country comparisons; within a given country, the poor and less educated tend to have more children than the other guys. (China might be an exception to that, I'm not sure.) From what I know of population trends in recorded history, this has always been the case.
This doesn't look good from an evolutionary point of view, if one is concerned with the long term instead of immediate x-risks and bioengineering etc. On the surface at least high education doesn't seem to be an evolutionarily valid tactic. Whether this applies for raw, general intelligence... Dunno. But I wouldn't be surprised if we'd reached an evolutionary equilibrium or a downswing.
the poor and less educated tend to have more children than the other guys. [...] From what I know of population trends in recorded history, this has always been the case.
I can't find the quote now, but I distinctly remember reading that before recent times (20th century or so), the number of children surviving to reproductive age and lifetime expected reproductive value were much higher among the wealthy elite than the vast majority of the population. It was said there that wealthy women hired poor nursemaids to suckle their babies, enabling them to giv...
An interesting new article, "Cooperation and the evolution of intelligence", uses a simple one-hidden-layer neural network to study the selection for intelligence in iterated prisoners' dilemma and iterated snowdrift dilemma games.
The article claims that increased intelligence decreased cooperation in IPD, and increased cooperation in ISD. However, if you look at figure 4 which graphs that data, you'll see that on average it decreased cooperation in both cases. They state that it increased cooperation in ISD based on a Spearman rank test. This test is deceptive in this case, because it ignores the magnitude of differences between datapoints, and so the datapoints on the right with a tiny but consistent increase in cooperation outweigh the datapoints on the left with large decreases in cooperation.
This suggests that intelligence is an externality, like pollution. Something that benefits the individual at a cost to society. They posit the evolution of intelligence as an arms race between members of the species.
ADDED: The things we consider good generally require intelligence, if we suppose (as I expect) that consciousness requires intelligence. So it wouldn't even make sense to conclude that intelligence is bad. Plus, intelligence itself might count as a good.
However, humans and human societies are currently near some evolutionary equilibrium. It's very possible that individual intelligence has not evolved past its current levels because it is at an equilibrium, beyond which higher individual intelligence results in lower social utility. In fact, if you believe SIAI's narrative about the danger of artificial intelligence and the difficulty of friendly AI, I think you would have to conclude that higher individual intelligence results in lower expected social utility, for human measures of utility.