If you're running a sustained campaign, set up your own list. Then send out a single message that calls for some action and include an advertisement for your new list. If you must send out multiple alerts on the same issue, make sure each one is easily distinguishable from the others and provides fresh, useful information. When the campaign is over, try to derive some lessons for others to use. Even if you're burned out, take a minute right away while the experience is still fresh in mind.
Good guesses are useful too.
An action alert is not an organization. If you want to build a lasting political movement, at some point you'll have to gather people together. The Internet is a useful tool for organizing, but it's just one tool and one medium among many that you will need, and you should evaluate it largely in terms of its contribution to larger organizing goals. The Internet is a democratic medium that provides us all with the time and space to do the right thing. So let's use the Internet in a positive way and encourage others to do the same.