I used to enjoy watching Nascar and F1 but now I sort of have grown out of it. I would say they are both fun in their own way and it is not the same. However Nascar has a very different problem than F1 that it relies heavily on nostalgia and the cultural bond of SOME people in the US, and in order to maintain this cultural bond we have some weird things like: "stock" car frame when nothing underneath is stock, V8 when it has not been the best design for stock car and same for carb engine till recently, over powered engine for the safety limit they have no idea of how to make things exciting yet safe at the same time, making things boring in the end because to the latest racing technology this race looks boring and nostalgic.
Eventually they will run out of fans if they keep trying to sell on nostalgia, like HD would run out of boomer buyer if the younger ones think they look too boomer if they are caught in one.
F1 has a similar problem when they ban a bunch of stuff like KERS and certain aerodynamics design, engine innovations that are available only in one manufacturer, etc, but they at least look a bit more fashionable and the international market is still there. The only "real" racing I watch these days are rally racing. You don't need to be too fast but all the jumping and dirt flying is exciting, accidents and car flipping all add to it too, even if it is going 4x slower than in a circle.