Alright, here's what I'd like to see, sorry if any of it is a repeat.
First of all, test drives! It seems to me that it would not be hard at all for you to pick a new or used car from the purchase screens, and take that car around some basic track for a few laps to see how it drives before you buy it. I've gotten really annoyed by cars I bought thinking they would be good, only to have them suck. Arcade mode isn't really an answer either, because a lot of cars aren't available until to you own them in GT mode.
Secondly, no "special cars". The Caterham Fireblade is an awesome car, but I can't race it against anyone. What a waste. Now, I don't think those cars should be gotten rid of, I just want to be allowed to race them. If I want to enter my 1936 Auto Union V16 Streamliner in the Euro Classic Championship, let me! I was so disappointed to find I couldn't race that car.
Third, give me a better way than previewing to know what cars are in the race so I can pick a car that will be a fun match BUT do not add more restrictions than are already in place. Sometimes, I want an even match, but sometimes I just want to get a race over with quickly to get some cash or to win a prize car, so let me bring a machine gun to a knife fight if I want to. Plus, sometimes, for all we say the AI is dumb, in some tracks with identical cars, it's nearly impossible to beat.
Which brings me to my third point. If there are going to be rolling starts, find some way to make the lineup fair. When the game puts the fastest car in the first slot, and you at the back, that's like starting the race 15 seconds behind, and then you still have to fight through all the other cars, while the leader car is cutting a perfect line. Maybe order the cars with the slowest cars at the front and the fastest at the back.
Finally, I like the idea of the tuner companies, but how about making them more realistic? Like not having the turbo kits from 3 different companies produce the exact same numbers? Give all the companies' parts different strengths and weaknesses, as well as prices, so that you actually have a reason to put on a Nismo turbo kit with an HKS exhaust. Also, they should not be JDM exclusive. I have a Dodge SRT-4 in real life, and I know for a fact that companies like HKS do sell parts for it.
Now, my thought on damage: Make it an option to be turned on or off. My one big fear with adding damage which costs money is that you could end up bankrupting yourself to the point where you would have to start over, or not be able to earn enough money to buy a better car and advance. GT4 was the first GT game I played(actually bought a playstation 2 just to play it), and if damage from crashing had cost money, I would have run out of money before I got through Beginner. Remember, we all sucked once. One thing I really like about this game is that you can't ever really lose the game, you just have to have patience.
And, of course, less Japanese bias. I like many of the cars, and I'm not asking for no Japanese cars. Just something more even. Do we really need 50 different Skylines, many of which differ only by the extra letters at the end of thier names? Sorry, but I just can't tell the difference between a "GTR V Spec II Nur" and a "GTR V Spec M1". Get rid of a few of those and add a 1969 Trans Am to the Pontiac lineup, please! Sorry, Pontiac just sticks out as a company that really got shafted (C'mon, the Vibe gets a spot but no Firebirds?!).
Also, how about an "Idiot Mode" for suspension setups? Let people adjust everything like now, but how about default settings like "Smooth Track", "City Course", "Curvy Roads", etc.
That's all for now... more if I think of it.
) for missions to start is 🤬... just start it with the other cars already ahead. 
