Sure there is...
highest price=best condition (like new or new)
lowest price=worst condition (parts machine)
I would argue that it's better then speculative condition, in a way. Also, if good pics are provided for a given sold game on eBay, I trust THAT over what some "guide" speculates is the current going price.
After all is said and done, completed eBay sales is just a "guide"
A yearly price guide is also just a "guide"
Your personal experience can also be a "guide"
Pinside forums/posts/asking prices could be considered a "guide"
Local groups to you, shows, leagues, ect. can also be a "guide"
All these in combination will give you the best information.
I will admit that the worst thing about the Boston list is that the more rare a game is to locate, the less likely the guide will help you in determining the potential value/asking price.