Does anyone have ideas for how one can rate the "effort "required to gain a given position on a given keyword? Such a formula would answer the question: what would be the relative difference in effort to get X or Y? If you know the value of having that position, you can gauge where your effort is best spent. The tricks is: the person asking the question does not have access to detail and depth of data the search engines have, and therefore the answer may never rise above "rules of thumb."
Some basic approaches:
(1) Look at the top position. How many links point to it?
(2) Look at the top position. What is it's PR value?
Clearly other factors come into account, eg.,
(1) how easy will it be to get incoming links in that topic area?
(2) compare the relative keyword relevance of your intended site with that of the top positions.
But how to weigh the factors, and put these into practice?