7 Newsletter Flaws
This article is aimed at non-profits, but I think there is a lot in here that applies to anyone trying to reach out to an audience. The take-away message I get is that you need to put yourself and your mission into the newsletter, instead of distancing your self from the reader. In a way, it's somewhat like writing a successful blog with a distinct voice behind it.
These Seven Donor Newsletter Flaws Are Killing You
I would argue not to go too far with these issues, though. While you shouldn't just throw statistics and charts into a newsletter, they can be used effectively to communicate important information. They should illustrate a point you're trying to make. But if it's just filler, put in a pretty picture instead.