The advances in auto racing safety worldwide are attributable to number of factors from driver equipment to car design to track safety features. HANS, track runoff areas, energy absorbent barriers and more robust driver compartments coupled with frangible exterior have been very effective in reducing injuries and deaths in the sport. Drivers and teams push it harder than ever before, relying on these safety features to protect them in the event of a crash. There are probably more crashes than ever before.
As it happens, little of this is directly applicable to air racing. Unlike auto racing, any safety gains made in this sport are made by preventing a crash from happening in the first place rather than by minimizing the consequences of a crash. As far as racing at Reno goes, I'd have to call the overall effort pretty successful considering that something like 18 pilots have died in crashes in all race classes since 1964. Considering the nature of the sport and the number of flight operations conducted during this time, 18 is not a large number.
This year marks the first time a spectator has died or been seriously injured in a racing accident. Certainly fortune plays a part in lack of spectator involvement in crashes before this year, but so too does the design of the race course layout and designated spectator areas. Undoubtedly, this will now be scrutinized as never before.
In auto racing, catch fences and barriers are ever more robust and spectators placed further from the action in an attempt to isolate them from the crash energy. Mostly it works well enough, though the next disaster could happen at any time and race organizers know it. They take the steps that are deemed necessary and continue to hold their races. Any risk remaining is deemed acceptable by everyone* attending the races or they wouldn't be there. Caveat Emptor
*Exception: children and others legally precluded from deciding for themselves.