First thing you gotta remember is that SDS very rarely adjusts defensive stats mid season.
Second - using your knowledge of the first above you need to look at if a player actually has room to grow. A good example of this is Nelson Cruz - his contact vs left, and power vs left and right are already at or near 100, his vision is at 67 - this leaves you very little room for him to grow and get additional 3 overall points. The same kind of logic can apply to Jesse Winker - he doesnt really have a tonne of room to grow making going diamond hard for him.
One of the easiest ways that i dont mind sharing is RP -> SP can actually very easily mean a rarity upgrade since going from 30 Sta -> 80 Sta can give a pretty big bump to overall.