15 years ago I sandblasted the rust on my 71 Cutlass before body work and paint. I brazed new metal on the perforated areas, then followed up with bondo, phospahate bare metal, prime, and paint. I've been driving it every summer since then, even in the rain. I have some bubbling where the corrosion used to be, but it's held up quite well for a DIY restoration - I couldn't expect any better. I think this car shows that sandblasting is a good method for restoration.
On the other hand, I sand blasted the corrosion on my winter car two years ago and it's back. This is the high wash area of the lower fender and it sees a lot of salt. Like I said, it's hard to duplicate OEM finishes. I'll be sand blasting it again, but it'll need some anticorrosion treatment like tar, which'll look like **** on a white car. But what can you do? The car is rustproofed, andt the corrosion I get is where the underbody meets the Class A finish panels - a no-man's land for corrosion protection.
I regularly sand blast automotive and other parts. I do it so often, that I'm considering getting a sand blast cabinet for the garage. I already have compressed air, gun, and an old, broken vacuum cleaner to vent the dust. I'm tired of using the sand blaster at work.
You say the Audi grille is steel? I haven't seen a steel grille since I don't know when. Usually they're plastic, pot metal, or trim metal (aluminum or stainless steel).