I like your original idea and would love to see it implemented in a future version of IPB. Could even do it similar to the "Currently viewing all posts. Change threshold?" section.
I see this happen a lot on my forums and others when a member uses the search function in regards to finding a download link for their search query. They find a relevant topic, scan through it and when they don't find the link they post asking about it. Its usually then that the member notices that the previous post was made X months ago. Now this wont help the first person but everyone after will notice the notification caused by the previous users post.
Just my 2 cents.
