I've been giving Heritage appraisals of my expensive instruments, which at this point are my Series I and my '67 Starfire that has been modified and also includes signatures of Phil Lesh and Jack Casady.
Serial numbers are also good. I think when it comes down to it, you'll probably need some purchase proof, receipts, etc. I've been insuring at replacement cost, so somewhere between street and MSRP. I had Mica send them a document for my Series I directly, so I think that got insured at list price.
Rusty, it's great you could do that! My State Farm rep refused. They said it was too high risk and would be really pricey.
Another option is Clarion, which I've heard good things about.