well grain is more difficult but acutance should increase with dilution but detecting the/any increase is debatable unless you are photographing resolution charts and using a microscope...
people who dilute Rodinal 1+100 or greater and stand are attempting to enhance acutance and reduce the grain increase you could get with more normal agitation.
I've not worried Im just mean and lazy 1+100 is cheaper and I set a timer and do other things for 60 mins.
I like grain