Back to the OP's original question, tailgaters should never be viewed as doing you a favor, aero or otherwise.
In aerodynamics, although the trailing car sees some benefit at not-entirely-unsafe-distances, this is relatively untrue from the lead car's point-of-view.
(This is from aerohead's magnificent trailer gap reference post that I keep citing.)
In terms of liability, I think traffic officers will almost always find the trailing car at fault for a rear-end, but I wouldn't take it as a given unless you run a dash-cam-DVR, i.e. you can prove that you did not swerve and/or brake-check. I see it as a big headache at best, also an opportunity to meet and greet with the most hot-headed segment of the population.