I couldn't say how much it would help........ I know 1/4" would be a waste of time. It probably costs almost as much as 1/2". You might be running into height issues with 1/2" plus the new flooring. Maybe not.
Have you checked the flooring for flatness?
........just a thought. Is this a single layer floor, like 3/4" tongue and groove OSB? If it is, I'm not sure if that's enough thickness especially being OSB. Some OSBs are better than others....... smoother and more sense.
OSB seams, if they are T&G, they are often puffed up, making a bump every 4 feet.
At the very least, take a 6 foot level or angle iron or angle aluminum, anything extremely flat, and check the floor for flatness everywhere, and especially the seams.