I don't know if this will make anyone feel better, but my DH sat in on some classes for law enforcement personnel re: possible terrorist targets in the USA. WDW and DL were actually pretty low on the list of possible targets because there are so many children there, and because of the fact that both resorts attract large numbers of foreign guests. If either one were to be targeted, the rest of the world would almost certainly join in the fight against terrorists and this would be strategically disasterous for them.
Added to that is the incredible behind-the-scenes security precautions at both WDW and DL that the guests just aren't aware of. DH toured their security sites several years ago (long before 9/11) and he was amazed at the lengths Disney went to keep their guests safe.
So there ya go - as far as safe vacations go - Disney is a pretty good place to be.
