The other side of the coin to this is multiplayer. With the way the current penalty system is what is to stop people from throwing all the go fast parts and nothing else then using other people as brakes or steering wheels. Granted, it can still be that way with cars that have been leveled up to unlock all the parts, but this method makes it much easier.
Everyone in a multiplayer race should have access to a car that can win the race if they're the best driver. That's just a basic requirement for fair multiplayer racing.
They should, of course, continue to try to improve the penalty system, as this remains one of the biggest problems for the entire concept of motor racing computer games where people are expected to race clean, a problem that GTS/7 also hasn't solved yet.
You've got two types of dirty driving - incompetent and malicious. Making people practice with the car they'll use for the race on the track the race will take place on won't help with malicious dirty driving. It would help with incompetent/accidental dirty driving, but the car level system is unlikely to help with that because people will either level cars up AFK, or if they drive them manually, they're driving them without the upgrades they need to be competitive, and as soon as they have the upgrades they want, they'll be competitive and don't need to spend any more time levelling the car up, so it hasn't been making people practice with the car in a race ready state. They also didn't need to practice the track they'll be racing on, they could level the car up on any track.
The most likely place where people will get appropriate pre-race practice is in the practice/qualifying session for the race, so it will be absolutely fine, as most people will probably try a few tunes in rivals first to find a good tune for the car, then they'll get some practice on the correct track before the race. If a tune is good (and if we're talking about a non-malicious driver, of course they've picked a good tune out of the ones they've tried, why wouldn't they), the dynamic driving line assist should let people become reasonably competent at driving a track in just a few laps. No amount of practice will help with malicious dirty driving, only a better penalty system can help with that.