David DeJesus has played eight seasons in the American League. Offensively, according to wRC+, he has produced above average in four seasons, and average or below average in the other four seasons. Much of DeJesus's offensive value comes from his ability to take pitches - he has seen more pitches per plate appearance than the league average in six of his eight seasons - and make contact - his Contact% is consistently 10% above league average.
However, much of DeJesus's value comes from his base running and fielding. As you can see from the chart below, DeJesus's base running and fielding combined have been more valuable than his hitting in five of his eight seasons.
2011 was not kind to DeJesus. He managed to only play 91 games, the fewest of his career, (not counting the 12 games he played in September of 2003), and struggled at the plate. DeJesus's 95 wRC+ indicates, that offensively, he was 5% below league average. His .309 wOBA was the lowest of his career, and his K% jumped to 17.0%. Some may suggest that the Oakland Coliseum is to blame for the decrease in his offensive numbers, primarily his wOBA. However, he essentially hit just as well at home (.307 wOBA), as he did on the road, (.312 wOBA). A more likely reason for the decline in his wOBA is the career-low BABIP of .274 that he posted in 2011. DeJesus was unlucky: the balls he hit into play just weren't falling as frequently as they were in the seven years prior. Using a variation of the expected BABIP (xBABIP) calculator created by Chris Dutton, DeJesus's xBABIP should have been .318 in 2011, .044 greater than it actually was. One can expect his BABIP to regress to the mean - his career average of .315 - in the near future, consequently improving his offensive value. Furthermore, though the increase in his strikeout rate and swinging strike rate is a concern, they were both still under the league average, while his walk rate was above average. These are all promising signs that DeJesus's 2011 struggles were most likely a combination of his injury - a surgically repaired right hand - and his unusually low BABIP.
In regards to the actual deal, the two year, $10 million deal the Cubs gave to David DeJesus is astonishingly cheap for a player of DeJesus's caliber. While the two-year contract may not be ideal, the Cubs are essentially paying for a 1.0 WAR player in 2012 and 2013. Even if DeJesus's production falters further from his 2011 levels, which is unlikely, it's hard to imagine DeJesus posting anything below a 1.0 WAR; thus, there is very little risk associated with this contract. The Cubs have bought low on DeJesus, and stand to gain a substantial surplus even if DeJesus posts numbers similar to his 2011 numbers. If DeJesus is worth 2.2 WAR/year over his two year contract, the Cubs will have gotten 4.4 WAR for the price of 2.0 WAR. If DeJesus bounces back to the 3.0+ WAR player that he has been at certain times in his career, the Cubs could be in line for a 4.0+ WAR surplus.
While this is a shrewd buy low opportunity that Theo and Jed capitalized on, this deal isn't very impactful. Last year, Tyler Colvin and Kosuke Fukudome combined to put up -1.1 WAR in right field. DeJesus in right field at 2.2 WAR, would net the Cubs about an additional 3 wins. 3 more wins for a 71 win team isn't very meaningful, but the type of player that the Cubs signed, and the contract that they singed him to, should provide hope to the fan base that the philosophy is finally changing. Theo and Jed coveted DeJesus for his patience and fielding back when they were with the Red Sox and Padres respectively. It looks like they've finally got their man, and at a price we should all be happy with.
Batting, Base Running, and Fielding Valuation: http://www.fangraphs.com/blogs/index.php/glossary/#winvalues.