The more I think and learn, the less I like. And not only just for the reasons Jim mentions.
Even contemporary mass products, like cars, are not all that well served by services like Kelly Blue Book. Invariably, from personal experience, these numbers don't jive enough with the situation on the ground to make them a basis for decisions.
Flux of demand and supply caused by the economy at large, regional variations, quirks and kinks in the pricing stemming from forum discussions, sudden shifts of fashion, etc. all make this less 'authoritative' and useful than I had hoped for.
Add to this the devil in the detail (re-chromed head basket, anyone?) and you get price fluctuations well into the double digits.
With other words: remotely done estimates of mic values are not a good method for getting realistic pricing.