I think the two are close but I believe the value nod goes to Dozier. The lack of a third year is an issue but there were concerns about Span's future production and fewer about Dozier's future production, IMO. In the three seasons preceding the trade, Span accumulated 7.8 fWAR. In the past three seasons, Dozier will have accumulated roughly 14.5 fWAR. In his final season with the Twins, Span was worth 3.4 fWAR. This season, Dozier is going to be worth around 6.0 fWAR. Dozier hits homers, lots of 'em, and does it from a middle infield position. Span is/was a table setter and a pretty good one. I think all of those things combine into a situation where teams will look at acquiring Dozier much more eagerly than they ever did Span. While OBP and table setting has increased in importance over the past few decades, home runs are still king, especially from an up-the-middle position. Though I worry about Dozier's position a bit. Most contending AL teams are set with very good second basemen, which limits most of the suitors to the NL. It's never promising when close to half the league simply doesn't need a player at that position.