Prolly for DIII its right on the borderline for useful/not useful~
wut is the difference between homegame incomes after loss vs. after a win?? If its more than the salary, well than its worth it I suppose.
The other question is does the boost help your team as much/more than adding another player/higher salary player.
The difference is often in the 20-25k range and occasionally more, so in those cases it can be worthwhile (even factoring the 1-2k to purchase the PR guy and the ~5-6k for severance for the prior guy). I look at increasing the salary/skill on my players more as a long-term thing than a game-to-game issue, so this is really my best way to squeeze a little more out of the roster based on competition.
But definitely I agree with the hypothesis that there's no reason to go for higher level PR guys, especially for lower level teams.