If you think you have something truly interesting to say then start a new discussion and link back to the old. This is how most people become aware of past discussions.

If you want to say something, feel free to respond to the old post. People who follow Newest Nodes or who use my Perlmonks Navigator will see the response no matter how old the post you are responding to.

BTW if you don't use one of those two you will miss a lot of interesting conversations...