Do you think RallyPoint should discontinue discussion threads after a certain amount of time?

Here is my thing in reality, 30 days is more than adequate. It's just sometimes people get busy, and then they don't get on for a while and so they respond to old threads late. Great idea to archive them, then people can look through them if they want to answer old threads.

What's the upside of closing threads? Closing threads would force multiple discussions on the same subjects by users that joined later.

Nah, if you see repetition highlight it to member admins to merge. If you have thoughts on an old enduring topic, have at it!

I think 30 days after the last response is reasonable.
And archive them if possible.