My observations based on driving my Westy in the snow:

1.  My Firestone Firehawk R4S 27x8.5 R 14 highway-rib tires are great in the
rain and in the dry.  They're not made for snow.
2.  Despite #1, the Vanagon remains very controllable and has a good deal of
recoverability.  The communicative steering enable me to keep the vehicle
within tires' low limits.
3.  Snow tires would help a bit to increase winter mobility and my
confidence.
4.  Given the vehicle's even weight distribution, tall stance, short
wheelbase and rear-wheel drive it is not that bad of a winter vehicle.  I've
had worse, like my old '75 Mustang II and '76 Cougar XR7.  I've also had
better like my old '87 Jetta GLI.

Chris,
'85 Westy
Usual disclaimers apply.