The Speedway was never a "unique experience" even when it opened in 1971. Most regional theme parks at the time had, and many still have, similar driving experiences. And many have even switched to using electric vehicles by now. Granted, many only have one track and not the 4 side by side tracks they have at MK, but other than that there is no difference (other than most regional parks having a more scenic route than the really boring Speedway at MK).
How many theme parks were there back then I wonder. Because pretty much every modest size city in the US has a go cart track now