* Make it easier to browse back in time. My biggest annoyance with news sites I've subscribed to is that they have no way to find articles after they have moved off the front page so I feel compelled to visit every day, and when I don't I feel like I'm wasting money, so I unsubscribe. I did eventually find that you have previous days available in the newsletter section, but a more discoverable interface like "previous/next day" link on the bottom of the page would be great.
* Add some less frequent newsletters, such as weekly and monthly which dedupe any stories that come up multiple times in that period, and include the top N stories, rather than everything over a threshold.
* Sections would be great for advanced users. My ideal would be to let the user set a different threshold for each section, but then still display them all together on the front page.