Have you tried cookies?
Otherwise you could just ask people why they are interested in Aikido. From their answer you may be able to figure out how to structure 'some' of the classes to address the interests of the various people who share them.
When someone leaves or simply stops coming you can ask them what their reasons are. As you said for the majority it will other life situations but for those that leave for reasons with something to do with the dojo (or person(s) in it) specifically... well, having a sort of 'exit interview' can help answer some of the questions you have.
With that information you can decide what you can do and more importantly, if you want to and if it is worth whatever effort may be involved.
But trust me on the cookies.
What cookies would you suggest you give potential students?Chocolate Chipped, Coconut flavoured, Milk chocolate, minty ones?Do you also provide them with a cup of cocoa, tea or a Starbucks special? Do you find the local cafes take umbrage on you for taking away some of their trade?Are you planning a food kitchen in the near future?I think soup and a crusty role would be a more effective ploy to generate interest than a cookie.