I agree with Jeff's last post, and I am speaking from experience.

I am not sure how much seat time you have but I am guessing not a whole lot(please correct me if I am wrong). My recommendation would be to save the money you would spend on Hoosiers and new suspension, and go buy a data logger and kumho victoracers.
I have been running on victoracers from the beginning and might upgrade this year(only because I got Hoosiers when they had the close out sale at $100 each). Who says victoracers are slow anyway, I have kept up with people running Hoosiers and Hankooks(only for my stupid accelerator cable to break with 2 laps to go)

I saved up and bought a data logger and it has cut off more time than I know Hoosiers would have, plus the data logger doesn't wear out. The year when I got my data logger I couldn't enter any races because of schedule conflicts but I did about 10 days of HPDE's at the same track, and boy did my times drop. Once my times got to a point where they leveled out and consistent from lap to lap only then did I start making changes to the car.

Another way to test if the car is at the max, is to let a more experienced driver drive your car. If they are faster than you, their is no real point in making changes until you reach that time.