I never pay much attention to the A-spec races, since, to me the real fun is in the Time Trials. It's such a pure form of competition where you can measure, to the thousandth of a second, exactly how fast everyone is, and who is faster than who, and just how fast and great of a lap a person can do on a track. I've always loved time trial racing ever since I was a kid (I even enjoyed watching the Qualifying sessions of F1 more than the actual racing itself, lol), and always felt it is the best, and most fun format of competitive racing.
As for the tracks and parameters, the only things I tend to really NOT like are the narrow tracks, and tracks that are too lengthy (like, ones that take 2 mins or longer are too long for me). I like tracks that take about 1 minute to complete (so, if it's like a 450pp event, then that would be a pretty short track, like Tsukuba or one of the "Mini" versions of some of the other tracks, etc), or for the higher PP events at 600-700pp, it can include some of the lower moderate length tracks, like Deep Forest (love that track), or Midfield Raceway, or some of the city tracks and also some of the shorter length medium or full gp tracks for ones that can be completed at 1 minute or near it at that PP level. I mean, that's just me though, obv there could be some variety to it, and occasionally have a narrow track or a lengthy track, since some people probably enjoy those, but, IN GENERAL I think the shorter length tracks that are wider are the ones that tend to make for the best TT competitions.
For 400-500pp events, I think I like Sports Hard tires the most, or maybe Sports medium or soft. Don't really like Comfort tires ones as much, just feels like sliding around on ice too much. For the higher PP events I like them on Racing Hard.
As for the car parameters, my favorite cars tend to be Japanese or European. I don't really like driving the American cars for the most part, I'm sad to say (even though I myself am an American), just never really liked the handling feel of a big heavy engine up front with rear wheel drive. I kinda like that really precise, tight feel that some of the Japanese sports cars and German or Italian sports cars have.
But, generally enjoy the moderate to moderately-light FR, and MR cars the most (and occasionally 4wd if it's a track I'm not as familiar with, or if the other parameters are brutal enough that it makes it tough to keep the car from spinning out. It just depends). I like the Nissan 350z and 370z, and the honda s2000, and the nsx's, and MR ferrari, and the nissan gtr and the bmw 3 csl/gtr and stuff like that, and for 4wd, I used to really love the audi r8 4.2, back on GT5, and also some of the WRX/Evo's I guess. But that's just off the top of my head. There are dozens upon dozens of other great cars in the 1,000-1,200 kg range from Japan and Europe that I also love to drive, but can't remember all off the top of my head. I just know it would be cool to get to cycle through a wider variety of different cool medium-light weight tightly handling Japanese/Euro sports cars more often, and not always get stuck on the GSX and nsx PROTOTYPE on all the 400-550pp events.
I LOVE the Honda NSX's of course, probably my favorite model of car in existence, the thing is just so low and wide and beautiful and precise, just a real engineering masterpiece, and extremely famous for how much passion they put into getting the thing to have great handling, as far as real life production cars go that you actually see driving around on the streets in real life, but I'm EXTREMELY bummed out that the top NSX in the TT events always ends up being that nsx "prototype" thing. Would be awesome if on all those events where that ends up being the top car on the "normal car" events, if they made prototype/concept cars not count as being in that car-category I think that would be GREAT (so, no more GSX CONCEPT car on the 400-500pp "normal car" events, and no more nsx prototype on the 550ish pp "normal car" events). I think most people would enjoy it more if the top go-to car in those 400-550pp non-race-car, normal-car events ended up being actual normal cars that us our our friends own and drive in real life. Like, both the GSX and the nsx prototypes are just prototypes, so there's none of that warm, tingly feeling in your tummy that you get when the top car of the TT ends up being some cool real world production car that we've all seen on the roads and isn't just some obscure "prototype" or "concept" car that we don't have real life experience and passion for, as fans of cars (which most of us who play gran turismo are, in real life).
Also really would prefer the Time Trial events to not be 4 weeks long. Preferably 2 weeks, or 3 weeks at the absolute longest. Or if they really HAVE to do this 4 week long thing, then they should double the amount (like, have 4 TT events at a time, rather than just 2). Having just 2 TT's and having them last for 4 whole weeks is just too scary though, because when you don't like the two TT's, which can happen a significant amount of the time, then you are screwed for a whole MONTH rather than just 2 weeks.
That said, I actually do kind of like having a bit longer to learn a track really thoroughly and try out more tunes and stuff, so, in some ways I do like it being a LITTLE longer than 2 weeks. 4 weeks still seems a little excessive though. I think maybe the most optimal of all would be to have 3 TT events at a time, and have their duration be 3 weeks. That would maybe be just about perfect. Because if you have too many simultaneous TT events (like, 5 or more at a time), then finishing high in the rankings starts to be less cool since there's too many different events going on for everyone to be keeping track of who the fastest dudes are at the top of all the different events simultaneously going on, so it kinda feels watered down/spread out too thin, in terms of the competition against the overall player pool, with the player pool getting split up too many different ways (i.e. if there was like 10 TT's going simultaneously or something, as an exaggerated example, the total amount of people putting serious time and effort into any 1 specific event would decrease per unit event on average), so, I think having 3 TT's going at a time, and having them last 3 weeks, would be maybe about ideal.
Also would really like it if they put in more filter options in the Online Leaderboard thing in the game for the Time Trials. Like, have it where you can sort by country, model of car, driving aids, controller/wheel, and so on and so forth, rather than the only two filter choices just being "Friends Rankings" and "World Rankings" and no other filter options beyond that.
Additionally, I think it would be pretty awesome if they could have like a menu option off on the left side of the screen when you are in the Online Leaderboard page of like "sector time rankings" where it would have like 3 little menu items on the left marked "Sector 1", "Sector 2", and "Sector 3", so for every TT event when you are checking the world rankings, you could move the cursor to the side of the screen and select one of those and it would open a new World Rankings page that looked identical to the main overall one, but for that specific sector of the track, and see what your own fastest sector time was for that sector, and how far down it is from the fastest sector time for that sector at the time, etc. I think that would be incredibly wonderful, and make the process of improving your lap times a LOT more fun. Especially if it had like a feature where it automatically totalled up your 3 fastest sector times and had a little blurb at the bottom-left of the screen, underneath those sector sub-sections things where it said like "Current fastest potential based on your current best sector times: _____". So like, if let's say in this Willow 600pp event my best 1st sector is 12.038, and my best 2nd sector is 14.754 and my best 3rd sector is 31.819, it would say "potential lap time based on your current best sectors: 58.611" in that example.
I'm sure there are more things as well, if I thought about it for longer, but off the top of my head, these are some of the things that seem most blatant to me as far as improving these seasonal Time Trial events (in my opinion).