Juan Castro has trade value. Color me surprised.
The Twins had way too many middle infielders on the roster, so this is a good move. Also, it means that the only person left to share time with Bartlett at SS is Punto, and as much as Gardy likes Punto, I haven't heard him talk about Punto seriously competing for the starting SS job. Getting Castro off the team makes it easier for Gardy to stick with Bartlett, and that's a good thing.
Why do you hate Castro?
I don't hate Castro, I just don't think he's very valuable. Additionally, he's most valuable when used as a spare part, but when thrust into a regular role, he drags down the team. However, getting the starting job wasn't his fault, that was just a poor judgement on the part of management.
How bad was Castro?
Castro was about 7 runs below replacement level on offense this year, while providing sub-par defense at a key defensive position. I don't know exactly how to quantify his defense, but I'd say that conservatively, he's been a replacement level glove. Basically, what Castro's done so far this year can easily be improved upon by a number of essentially freely available players, like, for instance, this guy.
Who is Brandon Roberts?
Well, I once knew a guy in grade school named Brandon Roberts. His best sport was hockey, though, and last I checked he was playing a minor role for Colorado College. I'm pretty sure he's not the Brandon Roberts the Twins received in return for Castro.
By the numbers, it looks like Roberts is a complete non-prospect. He hit .314/.370/.461 last year in the Pioneer league, which is pretty solid, but not really anything special for a 20-year old outfielder. He seems to be listed as a centerfielder, so it's possible that he's a plus defender there, which looks like the only thing that might give him any shred of value at the major league level.
This year, Roberts has hit .270/.328/.311, by Baseball America's count, in the high A Florida State League. That's a pretty poor line for a 21-year old in high A.
If Roberts can show the ability to play average to above average defense in centerfield AND he improves his results at the plate, it looks like he projects to be a 4th outfielder, at best. Probably something like what Lew Ford has done this year.
Of course, in return for a 34-year old utility infielder "hitting" .231/.258/.308, I wouldn't expect anything more.
In the grand scheme of things, this is really a pretty minor move. Castro wasn't in the Twins' future, they admitted that by bringing Bartlett back up to the big club, and now they are giving Castro a shot with a team that has a much better chance of making the playoffs this year. Consider it a favor to Castro, who for all of his shortcomings, did what he could to help the team.