According to who? I'm a bit wary of claims that seem to be a bit high. For instance in
this thread Robert posted that at 1500rpm engine friction accounts for about 4hp in a baseline 1.8L Honda engine. That's everything moving, valvetrain/cams, pistons, the crank, plus the balance/intermediate shafts. It seems unlikely that removing one shaft would cut friction losses by three quarters.
According to this the friction losses from the entire valvetrain are only about a quarter of the total losses. Realistically I figure a a balance shaft would be equivalent to a third of the valvetrain since the rockers are where most of the losses appear to be. That's what, about a sixteenth of the total engine friction, so a max of .25hp and probably a lot less?
Road load for a VW at 50mph is about 10hp, so you may go from 52mpg to 53.3mpg, if you're lucky. I think the oil pump otoh will net a more noticeable increase. What about getting some data with the oil pump out and the balance shaft still in, and then pull the balance shaft to see if you see anything? It's no A-B-A, but it's better than nothing.