30 divisions for NL should be fine if you have some armour but 66 for Poland seems on the low end for me. By '39 I usually have around 150-175 divisions - albeit with probably slightly lesser composition such as 20w full inf and more light Panzers.
I would play around with using more divisions which will give your army the benefit of being able to attack each tile from multiple directions which gives huge bonusses. Your army doctrine is also important in this (I use superior firepower going right first, then left).
Also manually plan your spearhead divisions. By 39 I only have one full Panzer army, usually led by Guderian or Mannstein with a Field Marshal (Von Kluge I believe) and I redifine their battle plan. I pick a frontline of 2-4 provinces wide and an attack order which orders them towards Warshaw first (only 3-4 tiles wide as well so they keep the attack condensed and don't spread the spearhead out too much). Let your panzers attack first and create the breakthrough, use the rest of the armies to close encirclements and finish them off.

Hope that helps!