Well, its a track car already if you just take it to the track! And as Alin sad, the best bang for your buck is experience.
Part 1:
So do this (seriously): Sign up for the very next autocross near you as a Novice. If you're paranoid about waranty and that somehow Autocross will void it (it wont) see below. I think an auto-x should be REQUIRED for any new-to-you car purchase. If you want to go one level up, sign up for an HPDE event near you. Even better experience by far, but much more expensive, all-in.
If you have no idea where to start to find an auto-x/HPDE, just google it with a city name near you or visit:
https://www.motorsportreg.com/ (no affiliation).
Part 2:
You can start to do suspension upgrades without worrying about what most people consider their warranty (engine). It's possible, but unlikely, that anything you do now you'll want to un-do further down the road as you become a pro track driver. Consider some swaybars and endlinks. They'll REALLY dial back body roll without making the drive noticably uncomfortable. If you chose right and/or get adjustable swaybars, you can dial out the massive understeer and really change the dynamics. Maybe research some springs and/or struts and/or coilovers. Many people want a lowered look anyways, so if you can get some extra performance out of them, why not. This isn't the freebee in terms of performance without harshness, so you'll want to do more soul-searching here. There are a ton of bushings/mounts/etc... that introduce even more slop that can be substituted to tighten everything up. But these, too, may introduce more NVH into the car, so know what you're getting yourself into. Depending on how you define suspension, you can look at new wheels/tires. Tires make the biggest single difference to handling, but as a consumable, they can end up getting expensive. Wheels provide looks and can also provide performance with new offsets, wider widths, weight, etc... Research will be your friend here.
Building off the weight savings from the wheels: a way to improve power-to-weight ratios is to remove weight! On my mostly-stock-power STI I had a fair bit of weight savings through wheels, carbon fiber fiber trunk, carbon APR wing...the whole list is in my journal. And there are some people who can go crazy with it. But if you dont want to do power, consider weight.
Finally the warranty/track thing from part 1:
How to 100% avoid any warranty issues for "racing" is to have a friend register for you (just so its in a different name) and remove your license plate as soon as you get there. Now no amount of googling, will turn up that you were there, nor will there be any photographic evidence of your car on a track doing some sort of "forbidden" activity.
I could use my car, but don't really want to F up my car by accident.
