I was wondering how I could add a sheen or sparkle to cakes and cupcakes without an airbrush. I have painted on luster dust before but I am looking for an all over effect.. Any suggestions??

You can buy cans of lustre spray, just like spray paint.
 

AI often combine luster dust with a bit of confectioner's and brush it onto my freshly covered fondant cakes. It leaves a very soft light overall sheen that barely shimmers. The advantage of doing it this way is it is very subtle. Brushing luster dust directly on can be a bit over powering and often does not go on evenly but mixing it with confectioner's sugar and brushing it on eliminated the problem.