Also don't forget the biggest terrorist attack prior to 9/11 against the US was not the previous (mostly failed) WTC attack, it was the two embassies in Africa (somewhat militarized considering every embassy has a wall and a detachment of marines) and prior to that the USS Cole. And a ways back we had the marine barracks in Beirut. Terrorists are not afraid of military targets.
http://en.wikipedia.org/wiki/USS_Cole_bombing
http://en.wikipedia.org/wiki/1998_United_States_embassy_bomb...
I don't fully disagree with the remainder of your comment, but I would also say that it's not a trivial factor that the targets you listed also have something else in common: they're all U.S. targets that are local or relatively easy to get to locations. Another consideration is that those are all older attacks. More recent attacks around the globe to Western facilities have focused on non-military targets. Based upon the result of 9/11 (U.S. engaging full force), the non-military target has demonstrated to be more productive for them.
The goal you stated for terrorists is not mutually exclusive with attacking economic and military targets. Bin Laden himself said that his goal is to bankrupt the US and attacking those installations would make a pretty good target for achieving that.
I can think of lots of other things that are vital to US economic interests. I don't think they're particularly hard to find.
Of course, thinking that terrorists want to target these things is a mistake; terrorists are not an existential threat to any state, not unless they have the sympathy of the general public and are fighting an unpopular government. As such, military targets are some ways down the priority list. Terrorists want targets that generate a disproportionate reactionary effect on the population. A pipeline in the middle of nowhere may affect energy prices indirectly, but lacks the immediacy that makes the public demand an overreaction.
Al Qaeda and the likes are more interested in regime change in Saudi Arabia than anything else. Making the US out to be the Great Satan plays into that dialog, and therefore making the US overreact, vilify Muslims, and polarize the population is their goal.