Hagerty writes both Stated Value and Agreed Value policies. They are not the same thing. If you have a Stated Value policy with the amount "Stated" as being $30,000, and you have a total loss claim, you will not be getting $30,000 for your loss.
Agreed Value are the ones that pay the "Agreed Amount" in the event of a total loss. An annual premium of $792 seems light for a $30,000 agreed value policy on a salvage title vehicle. You probably have Stated Value. Agreed Value policy premiums are more expensive than Stated Value policy premiums.
Hagerty is an agency. Not an insurance company. Virtually all of these classic car insurance policies are underwritten by three insurance companies that writes these policies. Hagerty is an agent for Essentia Insurance Company, which underwrites Hagerty's classic car policies.
I insure my Typhoon, and both Corvettes on my regular policies. With the multi-vehicle discounts, these 3 vehicles are about $250 each a year. No mileage or other usage restrictions. I have very low risk of loss because they generally never leave my house. Only the Ty and ZR-1 have comprehensive coverage ("theft") and the ZR-1 has collision (hitting something) because it is valuable enough, and I drive it enough and hard enough there is some risk of wrecking it myself, or getting hit in it. My 27,000 mile ZR-1's value is close to the $30k you have for your Sy. The ZR-1 is $230 a year for the entire policy. It would be a shit-fight to get an appropriate settlement, but there are several C4 ZR-1 sold on BaT every week. Easy to find comps. $230 beats hell out of $792. And no restrictions on mileage or usage.