first off, as has been said before, the car that you start with matters a lot.
new brakes on a car that can barely make it to 80 mph aren't going to be very
useful, and could even end up being counterproductive in practice due to the fact
that we're using controllers, not pedals (or at least not real pedals).
secondly, what exactly are you trying to do? probably cut down lap times, but
do you want every car that you use feel unique or do you not mind if they feel
somewhat similar. I'm looking forward to driving that volvo wagon because the
roll of it'll be unlike most the cars in gt3 (though I'm guessing there'll be plenty of
crap stock suspensions for the classic cars).
I don't own gt4 so this may no longer apply, but I thought that the lightened
flywheels (either sports or racing depending on the car) were really useful for most
cars. Maybe it's just a perception thing, but not only does a lighter flywheel boost
acceleration while on the gas, but it cuts down (sometimes way down) on the time it
takes to shift, something that could take a really long time in some of the early cars.
some lightening, a racing chip, and the carbon driveshaft were the other pretty
standard early purchases, because they're cheap and I know that I won't need to
replace them. If your car has some HP then brakes are another very important
component that you won't upgrade twice, and it sounds like they've become more
useful. I often skipped sports suspension because if I did upgrade I wanted it
to be fully customizable, but I wouldn't argue against buying it.
As far as the tire debate goes, beyond the fact that it sounds like tires aren't as
important in gt4 as in gt3, untill you get enough horsepower to get your car to the
point where even with smooth driving you still have to put considerable lateral g's
on the car, they don't necessarily matter all that much. Sure it doesn't take much
to get to that point if you're on a course full of tight turns in a car with decent
horsepower, but until you get to (I'm guessing) 150+ hp (depending also on the cars
weight) you're not going to be doing that too much. Also lightening the car has
the same effect as getting better tires which is reducing the slip angle that the car
is driving at, granted new tires will reduce the slip angle by more. weight reduction, however, has a couple of other benefits such as better acceleration, deceleration, and
other handling benefits that even a car with 65 hp can benefit from, and on nearly
every track. Well if you read all that I hope you got something out of it, cause that
just way too long....