"Watch a big shiny advert with really cool people in it. You can be like those really cool people ..."
I can see where you're coming from, but I'm still not sure this influences behaviour, but rather aspirational purchasing. For instance, taking that 'buy something that these really cool people have' example; sure, someone who doesn't fit that definition of cool may buy it because they've been sold the lifestyle, but will it mean that they then stop liking Warhammer 40k, and suddenly discover an inate raconteur within?
Okay, extreme example, so let's go back to cars. The advert has an empty road, with cars hairing round them without a care in the world; driver buys into the dream, sits in traffic jam because the road isn't clear, so okay, his behaviour might be influenced, but he can't actually attain that behaviour. Does an advert make someone pass a cyclist too close then left hook them without indicating? I have my doubts (but then I also don't think death metal and computer games turn teenagers into rampaging killers - which is the extension of the adverts-make-bad-drivers argument).
I'm going to pay attention to adverts over the weekend (not just car ones) and see what behaviours they could be creating, and see if there's any other product where it could be argued that those adverts do indeed create a general behaviour in a large swathe of people - if there isn't then I'd actually be more inclined to believe that with or without car adverts the roads would be exactly the same.