In my experience aikido demonstrations are only somewhat effective in attracting new students.
First of all, demonstrations easily atract those only interesseted in watching but with no intent to train at all. The only way these people contribute to getting new students is in being a source of "word of mouth" advertising.
Second, almost all people are not trained in seeing and understanding the things going on in the demonstration. This, together with an often found preconceptions about martial arts, makes them easily believe that aikido is nothing more than a soft bunnylike dance ritual. It was nothing like the bonecrushing and bloodspilling fighting they expected. Furthermore the cooperative and friendly way of training and practising is in their eyes suspicius. These problems almost all disappear once they joined (at least) one class.
Third, one might wonder whether the people that come to the demonstration are actually the people you want as students.
Just some thoughts.