Well, one major communication is between the event and your subconscious.
How can an event communicate?
Something happens with 666 symbolism in real life, and people react with much more fear because they believe it could the devil or Lucifer or Satan or whatever.
Pattern-seeking. People look for patterns in random events. Here's a hint:
If you look hard enough, there's always a pattern. Why? Because our minds are wired to find patterns. They look for things to say "aha!" about. That doesn't mean anyone or anything put them there. Sometimes randomness just looks non-random.
Consciously, and unconsciously even if you are not a bible thumper. And generating fear is really what terrorism is all about.
If what you're saying is that terrorists choose the timing of attacks to maximize fear, then you may have a point worth discussing. However, if the terrorists want to maximize fear, wouldn't they want to make the choice of timing obvious, rather than obscure? Say, attack on a few "holy" days or every second Monday for three months, or something we can easily see. That would scare people much more than what you've proposed.
Different numbers have a different meanings.
Yes, 1 means one more than 0, 2 means one more than 1 and two more than 0, etc. Beyond that, there's no inherent meaning.
Another reason for the numerology is that this is all part of the ritual, and that the illuminati are extremely superstitious.
Evidence please? Start with the existence of "the illuminati".
It's also a communication to people who are aware of the numerological meaning. It's like a big show off thing: look how powerful we are that we can arrange these things so precisely, and still no-one can challenge us, BWAHAHAHAHA etc. Keeps moral of the forces of evil high.
"No-one can challenge us?" Because they attacked on a date with no apparent significance, without warning, using a method the authorities didn't expect? Wouldn't that message be better sent by attacking again on, say September 13, 2001? Or at some high-security event like the Olympics or Super Bowl?
No, I'm not buying it.
P.S. You meant "morale", not "moral". By definition, "the forces of evil" don't have high morals.