I am kinda new with the pp system and how everything works here so i don't know whether it is worth it to go back a difficulty like 3.5 stars for pp. I can currently do 97.5% in 4 stars and anything above 4.2 stars i get a 94.4%-95.3%.
your highest plays give a bigger portion of your total pp than lower ones so it won't really give you much pp but it will greatly help you with improving at the game so you can get more pp later