I am going to be in the minority here. I think the Cubs need to hold on to Castro. Cubs have let to many young players go over the years on bad trades.
Quite the converse. Over the years, the trading away of Lou Brock is more than offset by getting young guys like Don Cardwell, Fergie Jenkins, Adolpho Phillips, Bobby Dernier, Ryne Sandberg, Keith Moreland--and that is just from trades with one team.
Closer to the truth would be the conclusion that the Cubs have had a poor farm system for years (except for the Dallas Green era in the 1980s) and for twenty long years did not produce a position player of stature--as evident from the lineup Theriot an average defensive infielder without power, Fontenot a decent utility infielder at best, Soto looking more & more like a one-year wonder, with below average defense, Colvin who should be getting at least a year of Triple A experience, and the first potential All-Star out of the system in twenty years--Starlin Castro--who hasn't been around the league once yet: the Cubs are a team that has lived, swim or sink, and mostly the latter, by trades and free agent signings--Lee, Ramirez, Fukadome, Soriano, Baker, Byrd, Bradley, Reed Johnson, Jim Edmonds, DeRosa, Michael Barrett, Jacques Jones, & all those others on & off the constantly moving carousel.
Even a parade of acquired pitchers--Dempster, Lilly, Silva, Jason Marquis, Lieber, Howry, Eyre, Gregg, Grabow, Gorzelany Rich Harden, Heilman, Maddux back as a costly free agent, and on & on. And this despite the only thing the Cub system could do for twenty years was develop pitchers...Prior, Wood, Zambrano, Marmol, Marshall, Dontrelle Willis, Ricky Nolascco come first to mind.
On the other hand, consider the long, long list of "prospects" that excited the Cubbie fan base and were held on to for much, much too long by Hendry (understandable to some extent, the desire to have a homegrown star in the everyday lineup). All the long, long list of hyped kids who a more astute organization would have packaged for established players--Felix Pie, Eric Patterson, Dave Kelton, Hee Seop Choi, Sean Gallagher, Rich Hill, Bobby Hill, Billy Petrick, Kevin Hart, Samardzica, Ronny Cedeno, Angel Guzman, Juan Cruz, Nik Jackson, and on & on goes the list of modestly talented young players the Cub front-office over-hyped and who Cub fans invested their emotions in.
A major reason why the Cubbie future is still bleak after 72 years without a real (non-wartime) pennant is that it seems to believe its own hype, holds on to "AAAA players" that the smart, well-run MLB organizations dump on unsuspecting General Managers in both leagues before they fail rather than after their shortcomings are obvious to everyone, even Jim Hendry.
Too much of the time the gullibility of Cub fans makes their relationship to Hendry & the team's ownership/management far to similar to Charlie Brown's willingness t believe Lucy won't pull the football back this time.
They still believe the hype: like the assumption above that the Marlins would be interested in an unproven rookie who at this time a year ago was struggling to get his average up to .250 in the Class A Florida State League.
Why on earth would anyone think the Marlins with an outfield of HR power Ross, Rookie of the year Coughlin, and highly touted Maybin would consider trading arguably the best shortstop in baseball for Colvin--especially when they have the problem of making a place in the lineup soon for the top OF prospect in all of baseball, 20 year old Mike Stanton.
But Colvin is an excellent example of the typical player Hendry holds on to too long. Package and trade him now, yes--but don't expect him to bring an everyday regular or a #4 starting pitcher EXCEPT as part of a package where his low salary accompanies a high priced player like Zambrano or Fukadome or Ramirez as part of the Cubbie massive remake of the lineup of a high budgeted team on the decline. Now whether the new ownership is too inexperienced or too naive to understand that the remake begins with replacing Hendry...good question.