I'll agree with that. There's a point of diminishing returns for the effort put into balancing a prop given that any remaining prop vibration would be lost in the noise of engine vibration. To balance, I always start by sanding the back of the blade across the whole width as best as possible starting at the tip because that's where it'll have the most affect. I tend to leave the top surface alone but it doesn't really worry me giving that a light sand because the aerodynamic shape of most props isn't exactly ideal anyway. Put it this way, you'll affect the aerodynamics of the airfoil a lot more by sanding off the moulding flash.