There is no average score. You should be safe with anything 100+ with extension 10k+ without on one word 75k+ with two or more. Anything on droplists below 100 with extension don't waste your money it's likely script created results. If a person says it has 30 OV/w and tells you it's getting about a unique a day it's junk and the one unique a day is a freak of nature.
Another thing to look out for is OV pump and dumps. If it's not a typo of a name with high OV with ext (and even those you have to be careful with) and the actual term of the name doesn't have any OV results at all then it's probably junk aswell.
As far as value is concerned it doesn't give much weight it's just a factor in determining traffic.