Insurance through a normal underwriter will value our cars at around $400, and if you have receipts for parts that are under 2 years old then you might be able to haggle for a small fraction of that as well. In 2007 I had a pleasant experience with Farmers where I had a heavily modified SCCA road race car that was totaled when another driver pulled a u-turn directly in front of me (on a city street). I was able to talk them up to $900 after an initial offer of $700 and change. The lowest price I could find for a like condition car without the $30k+ in modifications was $7k ... and it was way off in BFE in some forgotten state several thousand miles away. After several months of daily battles I ended up settling for $500 and retaining the car (now with salvage title) just so I could pull all of the parts off.
I WILL NEVER GO THROUGH THAT AGAIN!
My coupe goes to Auto-X events, and the occasional meetup ... and work once a year on 8/6. So I use classic car insurance which is an "agreed value". You have a ton of limitations on classic car insurance though. You must have a garage, clean 10+ year driving record, low allotment of annual mileage, etc.
Also, I actually pay about half of what I originally payed through my regular insurance provider when I first bought the car.
I do not use this particular insurance company, but this gives a very good explanation of the differences.
https://www.insureone.com/blog/your-classic-car-do-you-have-the-right-insurance/Hopefully all of that was helpful to someone...