Here's an interesting test from the Which Test Won blog.
For a travel industry e-newsletter, the test compared sending shorter, more frequent newsletters to longer less frequent ones. The total amount of content was roughly the same either way.
The less-content, more-frequency version got lower open and click rates, but much higher multiple opens and multiple clicks. More important, it got more purchases, revenue per contact, and less churn.
That's a pretty sweet deal. Look into the less-content, more-frequent approach to cultivating your email names. It just might make a difference for you.