[B]lowing the buildings up with explosives would be highly unnecessary to accomplish support for a war in the Middle East; the planes hitting the towers would certainly have been sufficient...
You're right. If a permanent military presence in the Middle East were the sole goal, the hijacked crashing planes would have been sufficient to motivate the public into supporting that action.
But what if one of the main goals really was the destruction of almost the entire WTC complex, the important records that were stored there, as well as the Office of Naval Intelligence in the Pentagon that was, ... oh, ... digging up dirt on the G.H.W.Bush administration?
What if the first goal was covering the tracks of their misdeeds in the past and using the shock-and-awe and misguided patriotism to spin it and rouse the nation into supporting even greater misdeeds? What if there were a way for this to cost them nothing, but to make money: through insurance claims, war-profiteering, and contracts and shoddy oversight of such contracts in the invaded nations?
Of course, you can't just destroy whole buildings and Pentagon wings without arousing suspicion. Get some airliners involved to give a plausible explanation for the "initiation of the collapse" (which was coincidentally, by the way, how the scope of NIST investigation into the towers collapsing on 9/11 was limited) and to add an element of "this could have been you flying", and you've got made to order fear that can be spun into overdrive to passing -- unread -- a massive piece of legislation named The USA PATRIOT ACT in just over a month.
"[N]ot only were the buildings targets, but ... specific offices within each building were the designated targets. ... [T]he attacks of September 11th were intended to cover-up the clearing of $240 billion dollars in securities covertly created in September 1991 to fund a covert economic war against the Soviet Union, during which 'unknown' western investors bought up much of the Soviet industry, with a focus on oil and gas. The attacks of September 11th also served to derail multiple Federal investigations away from crimes associated with the 1991 covert operation.
~ E. P. Heidner Collateral Damage of 9/11 (PDF)