To me, the most worrisome sign is the rapidity of turnaround time. I really doubt that the plan was "attack a group of tourists, and then when the delegation comes to investigate attack them." What this says to me is that, in Yemen, al-Qaeda is a group that can adapt quickly to their environment, and, even more worrisome, act without a long lead-in time. They saw an opportunity to make a splash, and took it. They were also able to produce back-to-back suicide attacks, showing a deepening level of commitment to the group.
Now, the flip-side of this is that they may, in fact, have had this plan all along- a long-term variation on the normal trick of having one bomb go off, then another when people crowd around to help. If this is true, it adds a frightening level of sophistication to AQAP's growing list of attributes.
UPDATE: As Greg reports, the delegation was leaving the country. This gives al-Qaeda slightly more lead-in time to the assault, but doesn't change the main point.