It would appear that Brian Duensing is headed for the Twins rotation, and Nick Blackburn is headed for parts unknown. (Or Rochester.) It seems less likely, then, that Duensing will be similarly supplanted via trade, and so the starting pitching question before the trade deadline becomes something different: what would it cost to upgrade from Kevin Slowey?
Allow me to ignore a few names right off the bat. Roy Oswalt is signed for $16 million next year. Dan Haren is signed for $12.75 million for both next year and the year after. According to John Bonnes, the Twins payroll is already shaping up at about $106 million next year - without Orlando Hudson or Carl Pavano, for starters, or any other free agent that might replace those two. Adding Oswalt or Haren would bump that up into the stratosphere. This seems highly unlikely. (And before you ask, Carlos Silva's $11.5 million for next year is an absolute non-starter. And it's also Carlos Silva, who would cause several notable Twins bloggers to commit suicide.)
With this in mind, let's compare a few of the others who might be on tap to replace Slowey. We'll use Fielding-Independent Pitching (FIP) numbers to do so, since those numbers only measure things that pitchers have demonstrable control over. Consider the following 2010 numbers:
You have been around long enough to know that one of these players, of course, is Slowey himself. The others, in descending order of FIP: Fausto Carmona, Ricky Nolasco, Ted Lilly, and Ben Sheets. And if you're waiting for the big reveal, here it is: Slowey is Player C.
Is it really worth it to replace Slowey, to give up assets, in order to get one of the other guys on that list?
This ignores a number of other potentially available trade targets, of course. You're welcome to examine others in the comments. But, as far as I can see, there aren't any options out there that are both A) a notable upgrade from Slowey and B) affordable for a team that's already nudging up against its payroll ceiling for next season.
No, Slowey hasn't been great lately - but the Twins likely can't afford to have five great starters. At the back end of the rotation, they may have to deal with a level that's better described as "Good enough. Sometimes."