I agree this was a surveilance mission, but I don't believe they were practicing to blow up a plane. The goal remains to take over a plane and kill thousands and not hundreds.
I think they still would very much like to take out the Capital dome in DC. The symbolic effect of that would be devastating, probably more so than the fall of the Twin Towers. So although I agree that they would like to do more than blow up planes, I wouldn't rule out blowing up planes as part of their game plan.