When talking about posts, one needs to separate base posts from replies.

Replies provide real world feedback and encourage actual dialog.

HF20 did a great job reducing spammy posts. Since they give replies the same weight as posts, they suppressed both new threads and replies.

PS: the best way to handle the resource credits for replies is to make comments thread aware. Adding a reply in a thread in which one is already engaged should not cost as much as creating a new thread or replying to t a new thread.