OBL -- and he's not the one I would most worry about when it comes to terrorist planners nowadays -- is less interested in, per se, attacking our centers of gravity than in:

a) getting us to engage in imperial overstretch of the sort told by Paul Kennedy in The Rise and Fall of the Great Powers;
b) seeing the alienation of the US from other countries in the world community; and
c) seeing the US government alienate and offend more people everywhere (including more of its own citizens and especially others).

Unfortunately we've fallen into OBL & Co's trap. And, for some time, we're likely not to get up easily anytime soon. "I've fallen and I can't get up" comes to mind for now.

OBL knows that a million dollars, a few committed persons and some "well"-peddled fear means we will respond with a few billion dollars in direct expenditure or -- perhaps -- even a trillion dollars in direct expenditures. Add in the indirect (and opportunity) costs and he's hoping for more of the same kind of dumb (high school-like) reactive/provacative behavior (and actions).

OBL's hoping the US attacks Iran .... so a terrorist attack that can bait the US into attacking Iran would be just what he'd order (if he has any direct influence). [And he's not alone in hoping for such. ] I'd start with thinking about what kind of fictional scenario would accomplish that sick objective and then work backwards if this was my cup of tea.