The general consensus on Navarro was that he could become a Mike Aviles type. Although he can play all over the infield, he doesn't play anywhere particularly well. He does a little bit of everything with the bat though. At 23, there is still time for him to become a major leaguer, but he's looking more like a utility guy. Kendal Volz was a mediocre starting pitcher prospect for the Red Sox, become transitioning to a reliever this season. Despite being 23, he's still in A ball, but he has struck out 56 in 51 innings this season. He's a long way from the majors, but could develop into a 6th or 7th inning guy.
Mike Aviles had a breakout rookie season, hitting .325/.354/.480, but has been a disappointment since. He had a disastrous sophomore season that was cut short by a forearm break, a bounceback 2010, and another disappointing season this year, only hitting .222/.261/.395. There are a couple reasons to be hopeful, though. In 2011 he has hit for a career high in isolated power (slugging percentage - batting average), and he's striking out less than the average major leaguer. He's been unlucky on balls in play (.231), but he also doesn't have very many line drives, which are strongly correlated with BABIP. All in all, I wouldn't expect great things from Aviles, but he should be serviceable, even at shortstop. Scutaro is dinged up and Lowrie is just about to begin his rehab assignment.
The deal fills a need for the Red Sox. If they don't make this deal and Scutaro goes down we're looking at Drew Sutton at short stop on a regular basis. Navarro in particular is likely to be a major leaguer, but he doesn't look quite ready yet. Long term, the Red Sox will probably lose this deal, but for 2011 it makes them better.