For the benefit of the original poster, redxr2...
The answer is; the engine will do fine.
There will be no improvement in your motor's performance. IF you do see a loss in mileage, the motor is evidently performing less efficently.
The washers are probably for shimming the spring in the diaphragm chamber, "part" of adjusting the valve.
The stock ABV is fine for quite a bit of pressure (certainly over 15-lbs). To my surprise a number of the failures I've seen seems to be the spring loses its sealing ability more than the rubber. second place is the diaphragm fails in the vaccuum chamber. Both usualy from corrosion.
These units were fitted in many cars of the era. Cars which boosted all day every day to 12-lbs. The B6T cuts electronicaly at 12-lbs. This is not the limit of the turbo, intercooler, plumbing, injectors, ignition, cooling, lubrication, pistons, etc, etc. nor the ABV
Stock ABV can be heard aside from mooing. The surge makes a flutter sound through the circut.
Compressor surge has little hissing in its sound as hissing goes.
http://www.youtube.com/watch?v=RaShaftq8_U I am assuming to clarify that redxr2's mileage may drop a bit, because the B6T ecu is not super sensitive. (I personaly cant confirm to the experiences of mileage that others have had)
I drove non turbos for some time and retained much of what I learned about turbos. My mods list won't show anyone here that this is true, its still true though.
**Rocketman please don't think I am a brat with any specific intent. I see there are matters where we post different pov's. I think thats great and you are just in many threads here. Keep posting plentifuly, you're more help than I am.