as above - it depends on a few things. for starters, if you're planning on keeping the car long term maintaining VW SH will not have much of an effect on the resale value.
but if there's an expensive failure VW won't help. that said, i doubt they'd help much now anyway as Mk5s are at least 5 years old. (but that said, the gesture of goodwill will ususally only bring the price down to how much a specialist would pay to do the same job anyway from my experience)
so my car, now nearly 8 years since first registration, is now for the first time having it's service done outside of the main dealer network. i feel that the added benefits of having the car serviced by a trustworthy specialist (in this case AKS Tuning who in my opinion is the best VW specialist bar none) will far outweigh any goodwill Audi may offer me at this stage in the car's life (even if it only has 67k on the clock)