I have updated the average WPA/AB for each position. The table below shows WPA per 100 ABs, simply because it's more readable.
To apply this data, I went through the leaders in WPA from 2004-2006 (the Top 20 each year). In applying this data to the premier hitters in the game I decided to use plate appearances rather than at-bats, as the best hitters generally walk a lot, and the large discrepancy between PA and AB will skew their adjustment.
Below are the 04-06 leaders in Adjusted WPA/100 PA, looking at the players who have finished in the Top 20 in any of the last three years. Minimum 1600 PA (Bonds would be the leader without this criteria, with a ridiculous 1.43 Adj WPA/100 PA.) Data taken from FanGraphs and Baseball-Reference.
The usual suspects. I was somewhat surprised to see Abreu on this list, but that's probably just because his power has tailed off over the last couple years, and this year he's not hitting at all. But all the walks certainly help.
The top 10 in Adjusted WPA over the last three years:
How is Bonds at the top of this list? A ridiculous 12.21 Adjusted WPA in 2004, which comes out to 2.11 Adj WPA/100 PA. Jeter gets a sizeable boost from his positional adjustment- he moves from 15th on the unadjusted WPA list to fourth on mine.
How does Alex Rodriguez's 2006 season look? A measley 0.69 Adj WPA.
The 2006 AL MVP race is also interesting. Jeter actually leads Morneau in unadjusted WPA (6.03-4.53), and after the adjustment it isn't even close (6.62-2.87).
Morneau is actually behind teammate Joe Mauer in Adj WPA (3.49-2.87), and Johan Santana's 4.12 WPA leads both of them. Not the BBWAA's finest moment.
Over in the NL the adjustment doesn't make all that much of a difference, as Howard and Pujols play the same position. The result is as expected- Pujols 8.04, Howard 6.88.