Okay. Let me explain this a little better. Some cars can be tuned by any of the 10 tuner groups in Gran Turismo 4 (mostly Japanese cars). You can buy parts for a car either from the manufacturer or the tuning group. For example, I could tune a Honda S2000 with either Mugen or any of the tuner groups in the Tuning Village that have parts for my S2000. When I meant "more cars to be tuned with original parts," that's because not every car you can tune in Tuner Village can be tuned with any of the parts original from the tuning group. I said "more cars to be tuned with original parts" because not every car that can be taken to the Tuner Village can receive original parts. I want to change that so that you get the absolute best aftermarket parts for any car that can be tuned in the Tuner Village as opposed to just getting parts from the manufacturer. Since not every car that can be tuned from the Tuner Village (as opposed to the manufacturer) has original parts ready-made for your car, I'd like more cars to be able to be tuned with original parts. You mod them up to be the best cars on the track on race day. Why not make an ultimate street car with this kind of package?
Try not to get confused reading this paragraph after reading the previous one. Something I've realized is that you still get basic parts from the Tuner Village firms. Just that only a few certain areas give you something completely original whether it's suspension, Stage 5 Turbo, or whatever. I think Tuner Village should allow you to get more original aftermarket parts that offer incredible performance equal or beyond manufactuer-offered parts. In other words, why get a Racing Muffler from Toyota Racing Development when you can get a high-quality Racing Muffler from somebody like Trial or HKS? Aside from Tuner Village specialists on certain cars, what about more companies that focus on specific car parts? Think of all the American car fans that would love to install a Flowmaster muffler to enjoy the sound of their V8 muscle? What about the sport compact people who want Tein suspension or something like that? Make Tuner Village more versatile and more open to a wide variety of cars.
In Perspective: "Tokyo Xtreme Racer Drift 2"
The mixing and matching of car parts (TXRD2) mostly pertains to horsepower additions. In Tokyo Xtreme Racer Drift 2, you can tune cars for horsepower by selecting pistons, crankshaft parts, and camshaft parts. Purchasing these parts to increase horsepower for your car is pretty basic. However, to get the most power from these parts, you must install car parts that will grant you the most horsepower. This doesn't come into effect until you purchase one specific part for your engine. After shopping around for one part, you'll begin to note that certain engine parts will deliver a shade more horsepower than the other four models (you can choose from five different companies). The key for more power was in getting the best compatibility of the parts.
This game has a feature I think would be pretty cool for GT5. Cars that are normally aspirated can have the option of installing a bolt-on turbo system. This will give your NA car a chance to enjoy turbo. From there, turbo cars can be equipped with an Intercooler, Turbine, and the Air Cleaner. Any car with a bolt-on turbo can give you the option to remove the bolt-on turbo to return to normal aspiration. Why would you want to modify a car to be a turbo? From my experience playing this game, I found that I could perform much better in race events and in drift battles by giving NA cars a bolt-on turbo. I would have never had such a great drift car (the Honda S2000) had I not installed a bolt-on turbo.
NOTE: If this idea does come along for GT5, equipping NA cars with a bolt-on turbo will disqualify you from entering the Normal Aspiration races. Get rid of the bolt-on turbo to compete in any NA races.
I also second the headlight thing. One button in GT4 was used for your "Special" thing, usually the Nitrous. Perhaps make it so that the "Special" can be used to turn on the headlights. Keeping nitrous means that players will need to reconfigure their joysticks so they can make room for turning on headlights and using nitrous.
As for sounds, I'm sure that the cars will sound better and perhaps more accuate using PS3 power. If not exact sounds, then at least something equal to "damn near accurate" sounds.