Thank you for your suggestions!
Rule-based sending is coming in the very next release which will allow you to send to lists based on search results, before and after dates, etc. along with a complex AND/OR system. I haven't yet thought about incorporating queries based on link-tracking, but I don't see it being too hard. This addition may not make it in the very next release as I've spent a considerable amount of time already on the ruleset feature and it is very powerful as is, but I will consider it again afterwards.
Statistics would make the program all that much more attractive and useful. I hope to have some nice reports in soon!