I'm not sure if you need to replace the whole ignition, I believe you can order a new key with a different RF signal output, and all you need to do is reprogram the cars receiver. It's not that hard to do.
Sure doesn't make one feel very comfortable, why would someone steal your key? Kinda makes me think they might be watching you and might hit you up again. If I where you I would install a switch on the fuel pump so only you know how to turn on the car.