One thing to watch for that has not been mentioned is how is the car valued. Most, if not all, main-line insurers use "actual cash value" for "ordinary" cars. In case of a total loss, that will pay you the depreciated book value, not what you probably want or expect.
For "collectable" cars, they typically want a photo or two and your estimate of the car's value to issue a "stated value" policy. That really just determines the premium you pay and the maximum amount they will pay you in case of loss. It is still subject to appraisal by an adjuster and you probably will get significantly less than what you expect.
Collector car insurers will sell you an "agreed value" policy where the car is appraised and they agree in the policy as to the value. In case of a total loss, you get that agreed value. The extent of that appraisal sort of depends on the value of the car. As long as your stated value seems reasonable, compared to a couple of photos, that is usually enough. Once the value gets fairly high (maybe $25k or more) a professional appraisal may be required.
Whatever you do, just be sure you understand which type valuation you get (actual cash value, stated value or agreed value) and what it might mean in the event you do suffer a total loss.