Probably the only tangible thing a change in allowance/ppm could really get you is exclusivity with SBs formerly uninterested in it. Intangibly, their entire attitude towards you might change, as they will mentally catalog you as a whale.
To your point - you can't change what someone looks like, you can't (significantly) change how available they are to meet, you can't change their personality, you can't change how well the two of you get along, you can't change what they like and dislike, in bed and in life in general.
That's why I don't negotiate. I know what I'm looking for regarding the above^ and what I'm comfortable offering, before I even know who the person is.