Tourism, in my opinion, will have a greater role in terrorism than it has had in the past. The average Mr. and Mrs. Doe will now been the subject of publicity seeking terrorists. The reason for the change can be easily seen. Terrorist are not stupid, or clinically insane individuals.
Terrorists can see the difficulty in attacking well-protected targets.
The answer, I believe, are the tourists. Tourists enter a country with the notion of seeing the land and the people. Quite literally, the tourist becomes the sheep going to his slaughter in a hostile country. He or she is very vulnerable to any and all types of attacks. One aspect that is worth not overlooking is the fact that every major international terrorist event has had, in some respect, the link of tourism.