This is not surprising, considering that these are physics and computer science rather than economics questions.

Hanson's paper is most useful for answering the question, 'if civilizations could expand at light-speed, would they?' There's 2 pieces to the puzzle, the ability to do so and the willingness to do so.

As for the ability: are you not satisfied by general considerations of von Neumann probes and starwisps? Those aren't going to get a civilization expanding at 0.9999c, say, but an average of 0.8 or 0.9 c would be enough, I'd think, for your theory.