Since I like putting specific numbers to discussions when they come up...

The TOTAL difference in insurance and sanction fee costs between a 'non-spectator Regional or National' and a 'spectator Regional or National' is $250. The costs are listed on the SCCA insurance rate sheets/sanction forms, both of which are on-line. No difference in sanction fees, just the liability insurance.

That $250 is a 'total' number. Not dependant on the number of spectators. Not dependant on the number of cars. Not dependant on the phase of the moon. "All in, all done". $250. Sold.

Clarity is a rare commodity. Just providing a small gift for the holiday season. You all owe me a beer.
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As John said, it's not much in the overall scheme of things.

Our race group buys the spectator insurance for every event not so much because of the thousands of spectators crowding the gates from 7 a.m. on (OK, so it's probably more like 6....people....trickling in all day) but because the spectator insurance gives us a little bit more CYA leverage with regard to the minor waivers and all of the issues that can come up with them. On top of that, our particular facility happens to have a dragstrip that is separate from the racetrack so the spectator insurance does the CYA for us in case some drag racers wander over towards the "good" side of the racetrack. :P

Jarrod