I don't think Nascar anywhere near as lucrative as it used to be for automakers, really in the last few years ratings and attendance has waned, problem when something gets so popular as it inexplicably did in the late 90s, an even bigger faction of the population realizes they just got duped into watching billboards drive around in circles for several hours, all while inducing tinnitus if you went to races
Nascar never really interested me in my lifetime, yes, including the 89-97 Tbird era. I have zero interest in seeing a spec frame run circles period, and it was already that way by the 90s. The car of tomorrow as I saw it was to eliminate what little differentiation there was that was left, throwing on a ricer wing to target "that" demographic(the subsequent elimination of it is proof AFAIC) and focus the light fully on the drivers, turning the car into the equivalent of a large helmet for them - Maybe I'm just weird, but when I'm watching racing, I'm watching THE CARS. I root for the car I like and applaud the driver for piloting it well, exactly as much as the crew for maintaining it through the race in fact. But I'm not a sports fan so maybe that's my problem. All I know is I'm the penultimate eat/sleep/live car guy, anyone who knows me can attest, and if I'm not drawn to a sport that is based around them, something is direly wrong.
I may not of lived through the era but it was far more interesting in the 60s. Manufactures truly were heavily involved, engine/driveline components actually were rooted from production offerings, and, as you mentioned, homologation was still a thing. The various 426 Hemi cars, Boss 429s, Daytona/Superbirds, Talledaga/Cyclone Spoiler IIs all existed on the street solely to make the engines and shapes eligible for racing - the latter of which now(especially the Fords and early Charger 500) are almost comical to think about in the context today with the very blatant sticker jobs on aero bodies being mandatory.
I think Tbird enthusiasts delude themselves a bit saying "Ford designed them for the ovals", the shape lent itself well to it, sure, but I seriously doubt Ford designers, feverishly trying to make a clean break from the slow selling boxy Iacocca approved 80-82s, in a world where European imports pretty had the styling reigns effectively handed to them, had even the slightest thought about how their new design would cope in Nascar, same with the MN12, which was more an E24 BMW crossed with an Audi 100, than a Torino Talledega homage.
Chevrolet was far more in tune with the Nascar crowd, they were the "heartbeat of 'Murica" brand afterall, who'se only takers by the 90s were the types who just loved that slogan and loved Nascar. Once they saw the success of the Tbirds over their broughamy knife edged G bodys, they pretty much took tracing paper to the Tbird shape and made the Lumina/Monte Carlos.