Well, Paris tourism seems to have gone up again, the Cologne carnaval seems to be well attended, and even London seems to have recuperated from the bomb attacks there some time ago :-)
Of course, if your life is going to be dictated by the terrorists :-)
I always joke with the airport security people that
(a) if someone wants to do an attack, no better place than the lines at the airport where your luggage is checked in or controlled
(b) I am sure the 9/11 attackers had shares in security companies.... Look at how the business boomed :-)
Nice place Istanbul.