Well.....time to put this spacer issue to rest.
In Germany EVERYTHING you add/change on a car has to be approved, documented & inspected by their Technical " Police " called TUV.
When your blasting down the Autobahn at Warp Speed, you don't want things falling off your car.
There are LOTS of people running spacers on their cars !
The consensus is, while it is not a good idea to use them in the front ( but they are approved ), you can use them.
I know for a fact, that Porsche uses or has used them on the rearaxle on some models.