With so many different niches and variables, I don't think you can slap a blanketed base-value sticker on domains. In theory, it sounds like it might work, however, It's my opinion that you would need a separate base value for every single niche/sub-niche. As soon as you cross over from one niche to another, the variables can alter the value dramatically.
For instance, you can't create a base value on a "Law Enforcement" domain and then use the same base value on an "Attorney" domain. The markets are completely different. Additionally, even with a domain like "Law Enforcement", the variables will slightly change again as soon as you sub-niche to say; "Law Enforcement Equipment".