Here's a proposal. Add the ability to filter out users based on their membership date. You could theoretically use this to associate yourself with people who have been around HN as long as you have. Even setting a minimum threshold to something like 100 days or a year would definitely reduce a lot of noise in the "new" section.

One of the best parts to me is the data is already stored and it has a very high cardinality, so it would work exceptionally well as an indexed field.