Not only was it imagined, it was planned in detailAt best, they scored only 3 out of four objectives, worst case I say they scored only 2 out of 4 since they muffed their primary objective when plane #3 opted for the Pentagon. I also say they scored below par in contrast to what the same number of *us* could do (on the basis of determination, ingenuity and competance).
Even less, I would say. There were credible reports of "dress rehearsals" that did not overlap with the 19 known hijackers, and plausible reports of other hijack teams on 9/11 that did not get off the ground or backed out of their missions.
Which brings up another point: Why 9/11? Why not 8/17? 6/3? The answer is, of course, that we can't know the logistics behind these attacks. Similarly, saying a nuke would already have been used if they had one is meaningless.