Dress code only applies to the paddocks, I believe, and I've walked in there in just shorts and t shirts before now, although I have not gone in on the Saturday or sunday.
We have always camped on MB, which is inside the circuit, and modern cars are allowed in, I think that this applies in the village area, which is not accessable by cars unless you have a special pass.
ACO are, I think, trying to create a Revival type event, as far as dressing up is concerned, without success, you can't tell the French to dress up if they don't want to.