If you have only done one track event it is unlikely your skills have exhausted the capabilites of the car even in its original form. I did my first trackx in my Lotus ( first 8 turns of our track vs. racing around cones) last fall and I felt like I was fighting the car. Truth is my braking/turn in points and throttle modulation were not even close to what it should be. Obviously my Viper was much different on the track and I needed to adjust my driving style.
If you go into a corner too late (typical for us beginners) it will result in a understeer condition and the car will feel like the front end is fighting to the outside of the turn. This loads up the front tires and the front end feels very heavy. The car is best when it is in an oversteer condition (back end it trying to swing loose) as the weight/HP will allow you to modulate the throttle and that will cause the car rear end to hunker down and avoid the tail end from coming loose. The old saying is turn in early and slow and you will come out smooth and fast. Then begin your turn in point deeper into the curve until you to get the perfect line . If you running out to track at your track out position your in too early, if your fighting the front your in to late........if it is smooth you know you got it right.
If I were you I would spend the money on a HPDE track day. The instructor will work with you on getting the most out of your car. Those stategies will transfer to your Autox events. The first time I tracked my car, I wanted to get all over it as you only have so many runs and you want to get the most from it. Better to take it slow, get the lines right and the speed will come. You may end up slower than the others now but you will eventually begin to CONSISTENTLY post better times than the ricers.
I also have a desire to upgrade the car, but first I am investing on upgrading the driver. For example, guys are spending $300 on a battery that saves them 3 lbs. If I could just lay off the dounuts for a week I could drop 10lbs and save myself 7lbs and $200. Then I could use that $200 to buy a HPDE track day. I beleive I will know it when the car is holding me back but I suspect that will be awhile.