FWIW, Hagerty is "agreed value" coverage. Even though you 'stated' the value during the application process, they 'agree' to your valuation when they write the policy.
I found Hagerty to be a little more $$ than some others, but I have several friends who have had claims with Hagerty and it was a no hassle process - they got repair estimates from their shop of choice, turned them in to Hagerty, and Hagerty sent check (payable to the policy holder). No hassles or arguing about valuation!
My car is insured for $50,000. A friend of mine just upped his Pantera coverage with Hagerty to $100,000 and they didn't bat an eye. His reasoning was that even if it cost $60,000 to fix his car properly, when done it would be a much better car than he could buy for $60,000 given all the work and upgrades that have already been done.