I like the Denard Span trade for many reasons. The Nationals have been looking for a center fielder since their inception and got one at the relatively low price of a minor league pitcher in Alex Meyer who has a ton of ML starting potential as well as bust/bullpen potential. I won't go further into the trade from a ML level since my colleague David Huzzard already went over that, but there are even more ripple effects caused by the trade when you look at it from a minor league and draft perspective.
The Nationals dealt away their second best pitching prospect (behind Lucas Giolito), but Meyer is much closer to the majors due to Giolito's Tommy John surgery. Despite being thin in high end pitching talent, Rizzo felt that he had the cupboard well stocked in the majors and some guys that could pass as ML pitchers in AA and AAA. The deal shows me that Rizzo has at least a little faith that Sammy Solis and Matt Purke can rebound from their injuries and make an impact in 2013 and that he believes that Christian Garcia or Ryan Perry can make it as major league starting pitchers in the long term. Losing Meyer is no small potatoes, but the Nationals have so much young ML pitching talent that it's not the end of the world.
What I love about this deal is that it allows the Nationals to reload in talent as well. Acquiring Span allows the Nats to choose between moving Michael Morse to 1B and letting Adam LaRoche walk or re-signing LaRoche and trading Morse for pitching help or prospects.
If the Nats decide to move Morse to 1B and let LaRoche leave, they will gain a compensation draft pick (38th overall). Gaining a supplemental pick is huge now because it allows the Nats the chance to add to their draft spending pool and potentially grab a pricier player with the 30th pick than they would have been able to if they did not have the 38th overall pick as well. In 2012, the #30 overall pick's slotted amount was about $1.6 million and the 38th pick was $1.36 million; the slot amounts could combine to be over $3 million in the 2013 draft, and the Nationals could then be able to spend $2 million or more on a player who slipped a little bit due to high bonus demands with the #30 pick and cut back to around $1 million for the 38th overall selection. Possessing a compensation pick will put the Nats in a good position next June.
Because Span costs so much less per season than guys like Upton or Bourn, I can see Rizzo putting the money not spent on a CF towards filling his ML pitching holes, and as a result I think he would move Morse for prospects/young ML players rather than 1-1 for an ML starter (just my opinion). They could likely fill the hole that Meyer left with a similar pitching prospect, perhaps even one closer to the majors than he was (although if that were the case, without as high of an upside).
Mike Rizzo did well to get a starting center fielder with a good contract for a pitching prospect who is by no means "can't miss." While I have the tendency to want to horde good prospects, I see this as a necessary and good move for the Nationals future, both short term and long term.