I also race karts and occasionally stock cars, and I've tried some of those preps on RC TC rubber tires.
The "qualifying" or "undetectable" preps are usually great for cleaning the tires, without making them greasy feeling. I've found these to be great on asphalt as you're not chasing a squirrely car on warm-up laps, and the seem to allow the tires to come up to operating temp quickly, and finish a run at a lower tire temp, without falling off in grip.
More aggressive kart preps [like the ones typically used by guys racing dirt oval] will dramatically soften a tire. Sometimes to the point where a hard spec tire will only last one race day if the prep time is too long between rounds. The first few mils of tire tread will shed off the tire in the first few corners on asphalt, which helps reveal fresh rubber for good grip. Without setup changes, this added grip can, at best, hurt corner speed, at worst, lead to traction rolling.
Some of the most aggressive kart preps, known by colorful names like "Goat Pee" and other similar mixtures, are really unsuitable for RC use. A lot of them have a combination of xylene and acetone in the mixture, which gives almost supernatural grip to the rubber, but will also cause your tire beads to come unglued, or melt the wheel.
I haven't used any tire preps that are applied inside the tire on RC tires.
I've used Hot Lap LMT
all summer on asphalt Rubber TC, on a sugar prepped track, and really like it. Doesn't unglue the tires, really seems to even out the grip throughout a run without dramatic swings, it's not so aggressive that I have to be super critical on my prep regime in conjunction with setup changes, it doesn't seem to affect tire wear, but it does lower tire temps at the end of a run compared with unprepped tires.
It's not quite aggressive enough for carpet, and since we're still a Paragon track, we still rock the black can.
It does decent on foam tires for 1/12, though I would be hesitant to try a more aggressive kart or car prep on foams.
Here's some other common tire preps used in kart and car oval racing: http://www.hdmworld.com/tirepreps.htm
Wintergreen is a lot like Paragon.
Goat P is aggressive stuff, it will dramatically shorten the tire life of most TC rubber tires, but it will soften them up.
Acrysol isn't used by itself very often, but it would probably work decent on RC tires to salvage a set of tires that have been glazed for one more decent run.
Speedy 500 is "kinda" like Jack or Sticky Fingers in that it will make the tire noticeably tacky, and won't stay on the tire an entire run, usually just long enough for the tire to come up to proper temperature.
Tire Tac is a great quick prep when you need to split tire durometers between what you have installed, and what the next softest tire you have available is. It's also decent for salvaging tires for that "one final run" that may have been glazed.
Of all of these, if I were to try something other than Paragon on carpet, Tire Tac would get my nod, but only after checking that it didn't unglue my tires, or melt wheels.
Bottom line is, if you want to try something new that's not marketed specifically to RC, don't experiment on your favorite tires, keep your old sets to test for safety first.
And the main question on these FTS preps, do ANY of the preps offered use Acetone, Xylene, or any other chemical than can damage CA bonds or plastics?