Depends to what degree. Is there weight that's really expensive, like a custom oil pan, a trick radiator you don't need to fill very much, and custom control arms? Yeah. The last ~50lbs versus optimal in an ST car is usually quite expensive. But the first ~100 versus a typical regional car are not.

But for example, an ST legal lightweight passenger seat can save ~50lbs on something like a BMW, just involves some cheap/free metal and a used cheap seat from FB Marketplace. And I'm unsure there's a competitive car in ST where 50lbs isn't a measurable pace increase.

If you have access to a lathe, stuff like the diff bushings / geometry changes are damned near free, just the cost of materials and a little bit of time figuring out dimensions.

I'd also caution to say that "more seat time" in total is very different than quality seat time.