His value depended a lot on where he signed. Manny in San Fran is a lot less valuable than in LAD.
Having said that, signing with the Dodgers makes him an easy 2nd round pick for me. Fenway suppressed his power with the deep gaps, Dodger stadium is more or less the perfect park for him.
Here is a quote from an article that ran on Feb 5th at http://baseballanalysts.com/archives/2009/02/
A popular image exists of the Green Monster adding lots of extra-base hits to a hitter’s total by turning shallow fly balls into wall-scraping doubles, but this hasn’t been the case for Manny: in the three seasons 2006-08, Manny only hit 6 doubles at Fenway that would have been outs at Dodger Stadium. Over the same period, Manny hit 23 flyouts, 5 doubles and 1 triple at Fenway that would have been home runs at Dodger Stadium.
Those results were found using Hit Tracker. Manny will be a monster this year if he stays healthy.