Why no Test Course, do you plan on finding your cars top speed at Sarthe all day?
As I tune a car for the track I wish to use it on,there is no need to know the top speed of an individual car ,only the best speed it will attain on the track it is being tuned for.For me, the test course serves no function in this case.And I don't enjoy making top speed runs on the test course,it bores me.
If the test course is included there will be those boring NASCAR style races in the events and in licensing ,which I absolutely can do without. The test course has no redeeming features for me.
As for the number of cars. If there where only 312 cars and the development time between new versions of GT was a "standard" 6 years,you would have one car a week to develop for a large number of tracks for the entire 6 years. And possibly more events as there would be more tracks to have events on. Not to mention the time spent on 2 player races and online races,I can't see how it would be possible to get bored with even 312 cars if there are many more tracks to run.
In addition ,concerning the number of cars, using online racing as an example,a good share of racers will use the car that proves to be the fastest at any particular track and the rest will not get used except by those that would prefer a good race rather than an easy win. This same thing ( guessing) probably happens in the events as well. There are those that would prefer a challenge ,but,I think they are probably badly outnumbered. There will also be those that have a few favorites they like to run ,everywhere . They would have more places to run them.
So,IN MY OPINION,a large number of available cars is more than it's cracked up to be,and a large number of tracks to run would be more fun for a longer period of time.
.......................Larry