As a visitor to IST, terrorism would be a minor concern for me too -- even as the marginal risks are now way less marginal than at this time last year. Still, the risk "can be marginalized further by staying in rented apartments, not doing the usual tourist things, avoiding crowded or popular sites and some other such approaches. But then there goes some of the fun of being a tourist."

No matter how relatively efficient the Turkish police may be, Turkey is in a hotspot situation/location given the domestic and regional/crossroad dynamics. Would I still visit Istanbul as a tourist this month or next month? Yes, if the weather weren't so lousy; but I would also expect a lot of people get turned off going this year in case a Paris or Bombay style attack hits Istanbul.