It's all physics.
Limit the speed capability and you limit the kinetic energy available for bad things to happen.
Restrictor plates are the easiest fix. Can be changed to suit individual tracks.
Spoiler is next best, but ..it's angle of attack limited. Backwards its not a spoiler anymore and downright dangerous.
NASCAR could mandate a smaller cubic inch rule..again ..
.. but them wascal engine guys would still get too much power out of 'em

'Back in the Day' highlights why they dont do '70's stock cars anymore.
Minor changes in directions overwhelmed the tires completely ..you could not 'recover' at all.
The drivers of the era talk about bein able to burn the back tires the whole back stretch ..them big blocks were mean an nasty

Ideally .. eliminate physical presence of spectators .. have it all big screen from a mile away.
No plates.
No fences.
Return of the big blocks.
'Off' run areas big enough.
Fastest guy wins -evil grin-
(can you imagine the push in the garages for more power, better traction, etc,

-GE (imagines a hi-tech 500+ cube Hemi truly blastin down any backstretch really pushin the limits.. ya .. come get some, Toyota)