It would certainly need a regular (annual?) update to the Insurance Policy, as everyone keeps adding to their collection, which adds to its value with each purchase.
And an insurance company would need to pre-approve your appraisal method... and as noted, I doubt there would be anyone in the world who's a "professional toy appraiser". The closest you'd get would be a professional toy dealer, and even then, your Insurer would need to recognise their "qualifications" beforehand. Perhaps being a registered toy business for a lengthy period of time maybe?