I think you've assured Homeland Security is currently monitoring this thread.
If you increase the scope of 9/11, expect everyone to go bats**t. I remember everyone getting freaked out 9/12, and that was only the World Trade Center with damage to the Pentagon. This just makes the horror more epic and devastates the nation in ways it hasn't seen since the Civil War.
Here's the thing though. Would more deaths make people go more "bats**t" that they did? Or in a less negative connotation, weren't people about as shocked and horrified as they could be?
I suppose there would be an added layer of instability if the attacks on D.C. took out more than just a couple of Congressmen (though we know Pres. Bush was away from D.C. reading to schoolchildren at the time, and would still be leading the nation).
Nevertheless, when it comes to thousands of deaths it is sort of incomprehensible to the human mind. To a nation that isn't used to attacks on home soil would 50,000 be all that more of a shock than 3,000. Much of the reaction wasn't to the exact number, but the fact that the bastards hit us. The oceans didn't stop an attack from reaching the homeland. Our perceived invincibility was shattered.
What would Bush have done any differently? Nobody was going to use a nuke. Period. Completely ASB even to suggest it. These are guys with bombs living in caves we're after, not a major military complex while in a total war with a major industrialized enemy capable of wiping us out. If nukes didn't fly during any of the incidents of the Cold War, they weren't going to fly then.
Everybody reacted as would be expected. People rallied around the President for a while. Patriotism came back in vogue for a while. The military went overseas to kick the crap out of some terrorists.
To me an interesting question would be, if the attacks on D.C. killed some Congressmen and Senators, how would this affect the post-attack bi-partisan honeymoon phase? Just one appointment/special election had the potential to change control of the Senate...