I've noticed for example that people's abilities to make good comments on LW do not seem to improve much with practice and feedback from votes (beyond maybe the first few weeks or so). Does this view represent an overvalue of intelligence?

That's interesting. I hadn't got that impression but I haven't looked too closely at such trends either. There are a few people whose comments have improved dramatically but the difference seems to be social development and and not necessarily their rational thinking - so perhaps you have a specific kind of improvement in mind.

I'm interested in any further observations on the topic by yourself or others.