Continue to reply to old nodes, you will at least get the attention of the person you're replying to (via the message in the CB)
and often the attention of people looking for new nodes and who will read your reply and the whole thread.

But talking about your solution, I wouls suggest something else :
A better solution would be (IMHO) to have the ability to subscribe to a thread,
and get a message each time something is posted on this thread.
(This idea isn't mine and I don't recall who talk about it first)

It has the advantage that you don't have to dig for new info on topics which interest you,
instead you just wait to receive messages when a topic you subscribed to is being posted.

"Trying to be a SMART lamer" (thanx to Merlyn ;-)