It's kind of hard to explain as it's apples to oranges, so it will sound greatly oversimplified. I tend to compare S2000 designs as this is the forum we're on. What formula 1 does doesn't apply to us. The aero characteristics of the car is a giant balancing act.

A lot of the rear downforce is actually obtained by the flow characteristics in the front of the car, especially the diffuser. Inwash using that high velocity air to energize the diffuser. Outwash uses it to avoid the high drag of open wheeled cars. Formula 1 cars actually have more drag than GT cars, but produce so much downforce their efficiency is greater. The reason we don't see much gain from a rear diffuser is that without a complete flat underbody, it's really hard to energize.

In conclusion, our wings don't see enough flow or high enough speed to benefit from the slats/gills. All they did was allow the low pressure air under the wing to escape, reducing downforce. The slats are also not very useful in 2D form, which is the only thing NASA allows. (I race NASA so it's the rulebook I care about)

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Definitely, agree that the speeds are much lower. And few of the S2000s are in competitive events; most that are in competitive events (other than autocross) are in classes where the gaps in lap times is measured in seconds. As far as I can tell, the rear wings are largely used just to correct a stock aero imbalance rather than add significant downforce.

Then it becomes a cool feature that might have a barely measurable effect. Similar to swanneck wing mounts.

Most classes that have the tight competition where the stuff adding tenths and twentieths of a second count have strict rules on the modifications that can be done. Even F1 would fit in that group, although its not quite the spec class of IndyCar and NASCAR,