The answer is quite straightforward.

C4D has no concept of real world units - if you have a model 200m by 200m and change the units, all C4D does is change the suffix. 

Vue on the other hand does know about real world units and scales accordingly. If you have set your Vue units to Meters then a C4D object of 200 units will come in at 200m. If on the other hand your Vue units are set to cm, the same C4D model will come in at 2m.

If your models are importing into vue at a very small size, just change the units in Vue to a bigger one.