In the era of asymmetric warfare, you can’t ignore the growing fundamentalist threat across all the Muslim world.
They get to pick the time and the targets while the army comes in to clean up and kill off the crazies afterward—but that doesn’t stop the initial terror event.
Egypt needs to stop posting guards -- they are nothing but targets, and that's bad for morale. They need help from an ally with expertise in drones, and go relentlessly on the attack. Setting up ambushes and remotely monitored traps, and monitoring electronic comm in the Sinai (because they're probably riddled with terrorist informants, who can then be identified and killed) is also important. But again, ultimately, the regime can handle the threat, not least because even among the jackass bro'hood supporters, most don't want to see the violent overthrow of the Egyptian gov't, or terrorist acts in the streets of Egyptian cities.