This strikes me as unlikely. Thieves steal for cash value, meaning something they can quickly turn into cash (TV, car stereos, or certain car parts).
The dealership tried to 'sell' me on anti-theft provisions, but I couldn't see the point -- nearly 100% of Leafs are going to be leased or financed (maybe a few people pay cash), so we are all carrying comprehensive insurance, and we are all under manufacturer's warranties. There is simply no reason for me to buy a gray-market part, and thus no reason for anyone to steal a Leaf for parts. And stealing one to use seems really crazy as well (a getaway car?), given the infrastructure and re-'fueling' requirements. So I feel like I have one of the more theft-proof cars on the road.
Given that the only market for the L1 charger is another EV owner (Volt, Leaf), and we are all in a position to buy/lease new cars, I can't imagine buying an L1 charger in a pawn shop.
I'm more concerned a thief would see the iPod cable and break in looking for my nano....