Personally, I don't see Autocross insurance as being an issue. When, if ever, have you seen someone prang their car during an autocross...even allowing for light pole contact or under-inflated tires leading to a roll-over? Personally: never seen either one. Over-revving the engine, scrambling the gearbox, flat spotting the tires - happen all of the time, but these are not insurable issues. I have seen policy references to exclusions for any "timed" events...therefore: TT's being a problem. Autocross? Hmmm. For DEs however - not so much, if any.
Over many years I've known only one friend that wrecked his car (a BMW) at a DE. USAA paid for the damage, then cancelled his insurance.

Maybe someone has more recent or relevant experience to share...???
Jim "
Old Guy" Dunlap
2017 Carrera 911 7 speed stick, Lava Orange

2017 Macan S, Sapphire Blue
2003 Morgan +8, Silver body with Dark Blue Wings