My opinion...convertible adds $$ to the "value", matching numbers adds $$ to the "value". Both add to the ownership experience. I'd say pay no more than 10% additional if it's in good shape for an ordinary car (not a T/A or something really rare) or less if not running as it may not really be rebuildable in the end. It all comes down to what are you willing to pay, because if you buy as an investment alone you're not going to make money. Also, if the engine turns out to be shot, you've just lost that claim for originality.

Jim, I like the sound of a $10,000 premium for a "numbers matching" car. My '69 is numbers matching, body, engine, trans and is as correct as I can make it. I'd estimate its value is only about $1500 - $2500 higher than a non-numbers matching "correct" car, and the insurance company doesn't care one way or the other.

If it was an extremely limited production car, like a Ram Air IV or a T/A, I can see that a big premium could be realistic if the car is valued at $40,000 or more. I don't think too many of us are in that situation