You would get more from simply swapping out your chainrings for newer, stiffer, ramped and pinned chainrings than gaining much between vintage square taper cranks unless yours is particularly flexy. I wouldn't bother. You probably won't notice a difference except for gearing. Technically there is some difference in weight and stiffness you won't notice unless you already notice it, which you don't. Some really strong riders might notice it and get some chain rub when standing. Higher end cranks used to be a little straighter, but at this point, it depends on the condition of the vintage crank.