I think that a large-scale retaliatory attack is just a show of force and a way to appease the public. Furthermore, if we attack Afghanistan we have to be prepared for more terrorist strikes back home.
In reality this should be an intelligence operation where all the action should occur behind the curtain. We should freeze the assets of known terrorists and especially people known to actively incite and fund terrorism. Most terrorist who actually carry out the operations are simply pawns, angry and misguided people who think they are doing the right thing.
We should also improve diplomatic ties in the region. We must put increased pressure on corrupt governments such as Saudi Arabia to help us track down terrorist instead of protecting them. Furthermore, we have to be consistent with our democratic message–Saudi Arabia is a very closed and oppressive society. The average income in Saudi Arabia is only around $7000 per year and yet this is one of the richest places on earth.
We should increase our humanitarian efforts in poor countries such as Afghanistan. In fact, I think the most poignant response would be for the US to take the money it would spend on an attack on Afghanistan (billions) and instead channel half of the money into building schools and hospitals for the country. This is the ultimate response! It sends a clear message to the people that we are not “evil” and this will dissipate all the Taliban propaganda that the US is the infidel enemy.
Naturally, we must also minimize our dependence on oil.