I agree. I've always personally believed that at least part of the goal of the anthrax was to try to deter or delay our retaliatory military response to 9/11. A mass anthrax attack killing a large number of people right on the heels of 9/11 would have put American support for an immediate, overwhelming military response at around 90-95% instead of just the 70-80% percent that it was.
I think they probably wanted to try to demonstrate the capability and means with which to kill number of people if they wanted to without actually doing so, which would have been the ultimate provocation. They didn't particularly care who actually died as a result though.