I respectfully disagree on both counts. I think a comment is always worth sharing, should you have the time and desire to make it. Whether or not anyone will see it should play no role in the decision making prior to making a comment. Again, in old topics there's always the option to tag people who have already contributed if you'd like to start a new discussion and you're worried that nobody will see it. My opinion is that a date feature would only add to people not contributing to older posts, and perhaps even from reading older submissions. If people only care about having their comments read, then they might even bother to read a post if they see the last comment was made 10 minutes ago. Who knows what they could be missing out on that point.
On this, I have to respectfully disagree with you. I'm not inclined to spend time and effort on something nobody will see. To me, tagging others in a post always feels uncomfortably like standing 6 inches away from someone on public transportation and then spewing my commens in their face, but perhaps I'm just not used to it. I am convinced, however, that the date function will push discussion towards newer posts, leading to an increasing rate of abaondonment of old posts. Maybe it's that I'm just not used to the culture on hubski that's much more discussion-oriented than I'm used to and that does value old content as much as new content. I'll try to keep that in mind in the future.Whether or not anyone will see it should play no role in the decision making prior to making a comment.