I'm a bit late to the party here (been quite some time since I've visited the forum), but thought I'd put my 2c in.
I started with a 2014 GT Track Pack. I replaced the dampers early on, with Koni Yellows. My reason for replacing them was the ride -- you could feel reverberations through the steering wheel when going over small (and thus high frequency) bumps, which strongly suggests underdamping of high frequency bumps. Koni Sports fixed this issue, which made the ride much better. Handling felt about the same.
Once I started to see the limits of the stock spring and sway bar setup on the track, which for me meant noticing the amount of time it took for the car to take a set after turn-in, it was time to change the suspension setup. This was particularly the case since at this point I had enough experience with the car to be able to control it under oversteer conditions, and found that I really enjoyed it, and thus wanted to change the handling balance to make it easier to controllably make the rear come out.
I'd always been curious about how a Boss 302 actually handled. This was my opportunity to find out. I probably wouldn't have done it if it weren't for the fact that the changeover was
dirt cheap. The springs were $20 each at the time (or thereabouts). The rear sway bar and panhard bar combined wound up being about $200, so the entire thing cost me about $300 in parts. In my case, I went with the standard Boss front springs and the Laguna Seca rear sway bar, rear springs, and panhard bar.
This transformed the handling of the car. Firstly, the turn-in became fast enough that I could no longer tell that there was a delay between turn-in and the car taking a set. Secondly, the car is noticeably more oversteerish than before. It's the handling balance I wanted: neutral at the limit with maintenance throttle (except in very tight corners, where it will understeer), but can induce oversteer either by lifting the throttle or by giving it too much. Yeah, it's probably not quite as fast around the track (or at least the autocross) but it's
hugely fun, and that's why I bought the car in the first place.
Bear in mind that the Boss 302 has larger tires in the rear than in the front, while my car (and most GTs) has a square setup. The handling balance is determined by all of the components acting in concert. So it's not a surprise in the slightest that the car has the handling balance it has. It would probably slightly understeer if it had the stock Boss 302 tire setup.
In any case, for anyone who wishes to retain the stock ride quality (in terms of ride hardness -- ride harshness is more defined by the dampers) but get significantly better handling responsiveness, and who doesn't mind a looser rear end, going with something akin to the setup I went with might well be the way to go. It's certainly inexpensive enough. Or, at least, it was.
Here's the information about part numbers and such:
https://www.s197forum.com/threads/k...ion-with-boss-302-springs.107272/post-1977066
The problem is that Autonation shows most of those parts as having been discontinued. For instance:
https://parts.autonationfordwhitebe...uZyZ5PTIwMTMmdD1ib3NzLTMwMiZlPTUtMGwtdjgtZ2Fz
At this point the aftermarket seems to be the only option. It might be best to make one change at a time, which in this case would mean (presuming the car is still fully stock) starting off with changing the dampers and rear sway bar, and see how it does, then change the springs if the handling characteristics still aren't to one's liking. An adjustable rear bar is almost certainly the way to go here since that will make it possible to trade off responsiveness against tendency to oversteer.
I can't say how much aftermarket options would be for the springs. I haven't looked. I rather doubt you'd be paying $20 each for them, so changing them might be a more expensive experiment than it's worth unless you've already experienced a car with the ones you're considering.