You raise an interesting point and I share with your suspicion.
Virginia Code Section 8.01-419.1 provides that the NADA value is admissible as evidence of fair market value of the value of an automobile in civil and criminal cases, subject to other "credible evidence" by a party showing it is not correct. (Kelley Blue Book does not enjoy the same imprimatur of legitimacy in Va).http://leg1.state.va.us/cgi-bin/legp...cod+8.01-419.1
The NADA values are generated by sales reported by the auto dealers, who tend to sell the cream of the crop (and who have an interest in boosting retail value and lowering trade-in). Accuracy is supported by a constantly high volume of sales and the competitive nature of the retail vehicle sales business.
The problems with NADA for sailboats are the much smaller number of units sold, compared to automobiles, and its reliance on the honesty and thoroughness of the reporting entities - the yacht brokers.
In addition, since the internet has allowed more sellers to bypass traditional brokers in the selling process, there are even fewer sales from which data can be drawn. While depreciation tables supply some abstract, seemingly accurate basis for supporting a given value, in fact, they cannot possibly account for the vagaries of economic conditions, which would seem to have a much greater effect on values.
Although some on this listserv disagree, I believe the best indication of value in the recession would be some discounted value of the list prices of comparable boats offered for sale, with or without a broker, because these boats represent a buyer's other choices and there is currently strong downward presssure on prices due to competition from an excess of supply.