Effect of reducing tire pressure for riding on snow All other factors being the same (normal carved tires, 28x1.40, paved road with 5-10 cm snow), does reducing the tires pressure provide any improvement for cycling onto snow?

My idea is that lowering the pressure increases the contact area and thus the grip.
Lower pressure for a larger contact patch to increase traction is common.  Cyclocross riders (for one) use low pressure.  

Weigh that against pinch flats.  As you lower the pressure you increase chance of pinch flats.  In snow the pot holes and bumps are partially hidden.

Tread type and depth will also affect snow traction.