Ingo > it is probably not worth doing the trip just for that, but it may be interesting to visit it if you visit the area anyway.
Note that most of the cars are pre-WW2. So I do not recommend it if you are more into newer cars (like me - it was good that it was free due to the ticket that I had from the autosalon visited in January).
I took pictures only of the Belgian ones and of a very large part of the post-WW2 that were there.