TR,
I see no real benefit to using these low SAPS oils in older TDI's...in fact I see no benefit to using them in PD engines. Once VW introduces their common rail engine with a diesel particle filter, you'll need to go that route.
The low SAPS oils are better for use in modern gas engines, however. So if you have a mixed fleet and want to use the same oil in both, this is a good way to go. See Busters post on the new (for North America), Mobil 1, ESP, 5w-40 which is a similar product to the Amsoil 5w-40/AFL.
TS
TS