More young people are going to be drink driving because their friend already had 1 passenger in their car. Drink driving obviously means higher road tolls.
About P platers not being able to drive turbo's, V8's etc, I think that's going too far. They should've just kept the old rule of not being able to drive a car that's 125kw/tonne, because power is power. Some turbo car's can't make power, but they still ban them. They should just have the 125kw rule. If you drive a turbo car and it goes over that limit or already is over the limit, fine them.
Hope that helps a little. It's all I can think of at the moment.