I also get a little tired of the attitude that until you are superstar behind the wheel changing anything is verboten. Sure, calling up griggs after your first HPDE is going overboard, but spending $1000 making some sensible modifications to improve what we already know is weak is not.
I'd like to know what you can learn on stock springs that you can't after 1.2" drop, or what you can learn on OEM shocks that you can't on Konis?
Okay, this is going to get a bit philosophical here...
First off, you DON'T need to be a superstar before you start modding the car, but a SOLID block of experience will go a long way towards realizing what pisses you off about the car, and how to fix THAT. Otherwise, you could wind up just throwing a pile of random parts onto the car, winding up hating what you have, but having no idea WHY you hate it, or how to fix it. So, another round of random parts, fighting the car, and then either finding a guy like Sam Strano to set you straight, or learning what works FOR YOU through pure trial-and-error.
A few examples:
1) The car pushes badly! I need coilovers, X5 ball joints, a bump-steer kit, and Hoosier tires to fix it. OR, just slow down a bit more at corner-entry, learn how to trailbrake, or start getting on the throttle a little sooner.
2) The car is wicked loose! I need a Watts link, LCA relocation brackets, a better differential, and Hoosier tires to fix it. OR, you could learn how to ROLL INTO the throttle, rather than whacking it down like an on-off switch.
In both cases above, we're talking about a stock car to begin with. In case 1, with poor entry technique, the only thing that will have any effect at all would be the tires. And all they'd be doing is masking poor driving technique. In case 2, the LCA brackets could easily make things worse! Again, the grip from the Ho-Hos would mask the poor driving habits, but are honestly not a fix.
When you get to the point of being consistently solid in your techniques, but find that you are limited by the stock setup, THEN it's time to fix the problems.
Let's revisit:
Case 1: The car pushes badly! But because I have experience, I now know that I have to brake earlier, get off the brake more smoothly to not upset the car at entry prior to turn-in, not to snap the wheel over like a hyperactive crack addict, but to get any mid-corner speed, I have to trailbrake heavily just to get rotation. Solution? Heavier springs to take the pitch-pole effect out of the braking action, and probably different bars to free up the rear end after the initial turn-in phase. Oh, and I'll need dampers to be able to control the springs.
Case 2: The car is wicked loose! But, because I have experience, and have learned the art of throttle modulation, I know that my issue is power oversteer, and not a component or geometry issue. Now that I have the corner entry figured out (see case 1), I'm carrying enough speed through the mid-corner phase that I don't feel the need to whack the throttle. Total cost: NO dollars.
The biggest factor is transferability. If you mod the hell out of your Mustang, and then learn how to drive the new platform with all it's good (and bad) manners, that does NOTHING for when you hop in a different car. If you learned how to modulate the brake and throttle, apply smooth but quick steering input, and know (from experience) how to read a track, you can hop into a Honda Civic, Nissan 350Z, WRX STi, another Mustang, a Z06, or a 458 Italia, and go out and DRIVE the car. You won't need the excuse of "I couldn't make the car go fast, because he didn't have Moton dampers..."
Long story short: If Boris Said could grab a bone-stock Mustang GT and whip ALL of our asses, in our highly modified machines, what does that tell you? Driver uber alles! Fix the driver issues first, and most of the handling woes will go away at the same time. Once you're getting everything you can out of the car, and you can identify a specific shortcoming (spring rates too low, I'll give you!), then you can change only what needs to be changed, with a minimal negative impact on the overall package.
I worked with a buddy about a month ago, with a 350Z. Bone stock except for Koni dampers and a StopTech brake kit with real pads. He was considering quite a number of changes, because he just couldn't get any transitional stability. I rode with him and his techniques were spot on, and the car just got loose on the switchbacks. We swapped seats, and I dropped his times by almost a half second a lap, simply by not downshifting through a particular section of the track. I kept it in fourth gear where he dropped to third, and because I had a smoother torque application as a result, I gained that touch of extra grip in the rear. I'm not any better of a driver than he is, I was just able to understand the dynamics
of a car I've never driven before, because I've been focusing on the driver mod, and not the car mod. In the end, it's about weight transfer, the friction circle, and figuring out how to maximize what you have.