Late reply, but I was speaking in generalities. HN doesn't quite fit the bill for a general forum that would improve from those tactics. There is a somewhat focused expectation of submissions, and the comments typically need a certain caliber of quality. Forums like this that deviate from those core tenets converge on being a Reddit clone with fewer users and features.
It's natural for users to engage less and less over time. However, holding the community to a certain standard keeps users from outgrowing the submissions and discussions. No one is too old, too mature, or too "smart" for earnest discussion.