Nuse isn't all the way wrong as we do use softer springs for low-traction situations (e.g. ice racing), but between different grades of summer tires, on most tarmac you can pretty much pinpoint an ideal range of spring rates to run, and that's going to be whatever gets you to a natural frequency of 1.8-2.2Hz in front, then:
For track cars, often the rear is setup in the same range, 1.8-2.2Hz;
For AutoX cars, often the rear is setup with >2.2Hz.
Neither AutoX or tracks are bumpy enough to the extent where the cars need significantly softer springs and damping forces; you pretty much need to be rallying to encounter that kind of bumps.
Because of that, on a non-aero car springs are chosen largely to affect weight transfer. Stiffer springs = faster weight transfer, and for the most part less maximum grip as the increased load transfer to the outside tires decreases the total grip level per axle. If you are driving fast enough at an AutoX, the corners are literally going to come up faster than the speed the stock spring rates can move the chassis. On a large track this is rarely an issue, and you can get away with running softer rates. This is the exact opposite of Nuse's guess.
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@bmspec Custom aero/suspension design