What if you have a neon light type of thingy on the top of the page that flashes "new features". When someone clicks on it, it shows anything new that has been added. The flashing goes away once the person has clicked on it.
Maybe what should be done is to keep it off by default for all existing users. When a new user signs up they should have a check box that allows them to select whether they want those e-mail messages or not. That would be similar to what happens when you sign up at most sites and they ask your preferences for e-mail communication.
I say leave the default as ON...those who don't want it (ie the people that have no life per MATTY...thanks, Dumpling) merely have to turn it off once & it's gone forever...for newbies to the site or those that don't hang here all the time, it might be a good thing...