Both Bush and Cheney have major interests in energy companies. Enron and other major companies loaned the Bush campaign the use of their aircraft during the Florida fight. They donated alot of money to the Bush campaign otherwise.
You've heard of political payback haven't you? The reward occurs after the administration leaves office. Always does. Look at how many ex-Senators and Congressman are lobbyists for industries that courted them while they held office. Furthermore, in this case, the Caspian pipeline was a pipe-dream for all intents and purposes due to the instability in the region, namely Afghanistan. While I would never claim that 9/11 was staged in order to facilitate the Afghanistan nation-building occurring now, it is quite obvious that the results are favorable to those who thought the pipeline all but impossible.
In fact, I don't think the administration would stage such an event given their obvious belief that the American public will fall for outright lies as justification for going to war with Iraq.
In fact, the action in Afghanistan was already planned prior to the events of 9/11. The press in India had reported that Afghanistan was to be invaded as early as July of 2001.
9/11 simply saved the administration some lame excuses to draw from. As it was, there still wasn't any justification for invading Afghanistan (Al Quaeda is NOT Afghanistan nor is Afghanistan Al Quaeda).