Castro is a good hitter at a premium position. His D is not as good as some, but better than he gets credit for.
They were discussing Castro and shortstops on MLB the other day. (Russo, the New Yorker) They had a list of the Top 10 SS selcteby some publication, and the host was questioning why Castro wasn't there, and essentially said he would choose him over just about anyone else on the list after Tulo, and the co-host agreed except on Reyes of all people.
Russo was singling them out by name, and asking the co-host "Would you really take "X" over Castro?" in a way that indicated that not only would he select Castro, but found it inconceivable someone might not. Right down (or up) to Peralta, who for some reason is rated high. Average D, average bat. Big salary. But plays for Cards, so highly rated.
Now I don't put Russo's opinion above any other pundit, but was pointing out that clearly there are people not in Chicago or tied to the club that value Castro.
I know a lot of it has to do with when you get called up, but the kid has 850 hits at age 24. he had an OPS of .777 at the SS position. He is valuable!