AQ's first post-9/11, post-anthrax attack was on a synagogue in Tunisia that killed 13 people. Not exactly the kind of high profile target you're talking about. The DC-area killings are getting more coverage than anything they've done in the past year (since the anthrax trial balloons). Coverage is what they crave.
Not every terror attack is going to be 9/11. Just look to Israel for proof of that. I believe they bombed an ice cream parlor, killing a single infant, just a few months ago.
To think that their playbook is limited exclusively to large scale attacks on highly recognizable targets is flat-out inaccurate.