I believe in defensive value. When a player is better than average at his position he will give you positive value and when worse than average he will give you negative value.
I even believe positions like SS and CF give an elite player more opportunities and thus they have the possibility if good enough to have more positive D value than others. And a truly bad player at these positions conversely could have a bigger negative D value as well.
I also think there is value in these positions because come trade time usually there are more players available at lesser D positions, but this is not always the case.
What I've not understood is intrinsic D value in the position itself. This definitely works in roto baseball.
I guess my question is this: If your team goes out and spends $25 million per year on a player like Mauer or Hanley Ramirez are they getting D positional value to go along with the bat? In Mauer's case they will get D value where he is over and above the average catcher. But do they get value in his being a catcher?
Many will use replacement level but there are many serious problems with this. First of all replacement values are high - almost average player high.
My example is this: Pujols or Mauer. It's not perfect. But if your team could add one for $25 million which would help your team more. Let's assume Mauer hits like he did last year. Many would immediately assume Mauer because he is a catcher and their team might have a star 1B already. But when you look at true value - adding Pujols would then mean taking Pena/Tex/Papi/etc. off the books. And adding Mauer would mean taking Varitek/Olivo/etc. off the books.
So immediately we see the big offensive upgrade on Mauer. But we only take a 1 or 2 million contract off. And a lesser impact adding Pujols but then taking a 15 million or so contract off. While replacement players might be better at less skilled positions I think their contracts offset this. And this matters to most teams in the majors. Even the Yankees have 2 fairly weak hitters in their lineup, and that is with stars in their skilled positions.
I do believe there is a small amount of value in flexibility and scarcity at trading time. But not much other than that.