Different tournament structures are one way to bring people back in, but there must be others.
I would imagine that giving away free, super-streamlined decks at Magic tournaments would be the best way to get new players. For the cost of 45-49 playing cards (next to nothing to manufacture) you put a fun card game designed by Richard Garfield into the hands of the exact people who are into that right when they have downtime to mess around with it. (Not to mention disposable income to blow on it.)
Like any addiction, just make the first hit free.