only assuming that the low oil pressure is due to the relief valve being open, which I've never seen to be the case. If the oil pressure is low at idle the spring wont help. If its low at 40 mph because the relief valve is open, a stiffer/longer/shimmed spring would help
That's not been my experience in all cases. I, like some other members, have an adjustable spring cap on my oil pump. I can dial in pretty much any idle oil pressure I want by increasing or decreasing the tension on the relief spring. The change in tension affects the pressure all the way up the rpm range. I will concede that if the low idle pressure is caused by excessive bearing clearances or worn out pump gears, the tension change won't help.