Bob, I worked for VW/Audi for 7 years and like all large international brands they are very image conscious.
Their worldwide reputation was tarnished immensely over the emissions fiasco .
They would not issue the resolution unless it was 2000% with no effect to driveability, economy, etc etc.
If the resolution fails, then the damage to the brand name may well be irreversible.
If you are concerned about the resale value of your car with the modification, then to play devils advocate, what would the resale value be without the modification?
As others who have the modification completed have said, they have seen no effects, so if I were in your position I'd go for the modification.
You'd get a warranty on the parts/modifications fitted and possibly use of a free loan car (if you play your cards right) while yours is under repair.