If you just want to murder a lot of people and cause panic you would be better off poisoning the food chain or worse the water supply. They like high profile events but I really don't know what the really think they accomplish with tis sort of stupidity beyond increasing hatred and prejudice towards other Muslims. As tragic as these events are thy will never come close to causing the West to be intimidated into giving in to them.
I know it does motivate the borderline radicals in their community before that is all short gain crap that will eventually lose it draw as more and more of even the radical Muslims realize that they are the biggest victims of this. It works in the less stabile Muslims nations to make them even more unstable but that is about it.
At some point we are going to realize crushing nations which support and then skipping the rebuild step is going to be required. Crush Yemen and give them to Saudi as a new state. Crush Syria and Divide it up between Turkey and Jordan. It isn't like they are real nationalities anyways.