What is being suggested here is a cartel. Yes, if one city didn't agree to signing up for the non-aggression agreement at all, they may stand to win, but if everyone agrees on non-aggression, then whomever the eventual winner is wins the deal for much cheaper. Of course, in practice, defining what constitutes aggression and tax cuts would be quite difficult, but in theory players competing in a winner takes all market could still work.
More relevant to the topic under discussion would be a future where cities go to war to keep each other from winning the favor of massive corporations.