I have been several times and if you like old cars it is not to be missed.  

I sold my beautifully restored Karmann Ghia there two hours after I arrived.  
There were Japanese and European buyers there early in the morning with
flashlights to check out the sale cars when they came through the gate.

It is quite a mixture of cars from old rusty junk to mint rare autos
trailered in.  I have seen only a small amount of Vanagon items offered there
but there is a huge VW section, mostly air cooled.  

One item I found there is a pin dealer that sells vanagon pins in 4 different
colors.  There are venders of old repair manuals, auto advertising items,
brochures, toys, etc., just about anything related to cars will be there.  If
you like this kind of thing bring a camera and a kids wagon (for hauling out
all your treasures)!

If you are selling, get there early for the best spots, many people camp out
to get the best position to sell their cars.  Plus there is the no extra
charge for your passenger, I think it is 15 to sell or show so if there are
two of you going it would be a better deal just to show your car, that way
you'd get a better parking spot too.  I think the car has to be pre-1975 to
get in though.

Have fun & hope it doesn't rain!
-Loretta
87 Syncro GL
90 GL