Of course all smart event organizers track key metrics like registrants, attendance, budget, and profit but many times those metrics are never tied back to the individual marketing campaigns. While it may be easy to smile and say the overall goals were met - we were a success, it is important to take another look at how they were met. As much as possible each piece of public outreach should be able to be measured.
Emails -- Which emails got the most opens? Was there something different in those subject lines? What was the offer within the email? Was there a certain time of day or week that performed better? Find the common ties between the high opens as well as the commonalities among the low opens. For future events, do more of what worked and less of what did not.