Anyone who is active in buying/selling websites mind telling me how accurate the "estimated value" feature is in this tool?
The estimated value is not useful for selling domains. Buying domains is a cut throat business where buyers try to get top domain names for pennies or they try to actually steal the domains by bribing hosting company owners to delay renewals so the domain names can expire and they grab them. IMHO selling or buying domain names has become a real dirty business. My advice is stay out of domain selling. You only expose your good domain name to the sharks.
Although the dnscoop might give you some useful statistics about your website, don't get carried away entirely by the results. It is not exactly correct. The next update that is shown in the statistics is for the dnscoop to reassess your website for its worthiness and has nothing to do with the google PR update as suggested by our friend mrlynam. Wait and watch for the real google PR update. Don't know whether it is worth waiting?