1) The team is right when it says it's done its major acquisitions.
Kenny's bought 5 guys for the 25 man roster in Vizquel, Kotsay, Jones, Teahen and Pierre for about $9M. That's 1.5-2 expected WAR, which they'll probably get. But the Sox aren't leveraging themselves one way or another based on the performance of the supporting cast.
2) The 2009 White Sox opened the season with 3 very specific deficiencies: 3B, CF, and Starter Candidate #5
Consider: Last year's 79-80 win talent was basically without Rios, Beckham and Peavy and (though Rios didn't help much) the former two had collectively below replacement antecedents in Fields, Betemit, Anderson and Wise. Peavy meanwhile replaces the 4 starter amalgam worth probably 1.5-2 WAR in '09. So let's say Rios' value is 1-3 wins over '09 replacement, Beckham 3-4, and Peavy 1-3. That's 87-88 wins total.
3) True Talent In '10
Eyeballing it, CHONE has the Sox winning 87ish games, ZiPS a couple fewer while Bill James and the fans (perhaps expectedly) are the most optimistic. So the Sox right now are baseline in the 86-88 win range.
4) The Sweet Spot
Nate Silver, from Baseball Between The Numbers:
The most sensitive part of the graph--what we'll call the sweet spot--is between about 86 and 93 wins.
Kenny undoubtedly has his own team-specific version of this general calculation, but the suggestion from here is that it probably makes a certain amount of economic sense for Kenny to nab a DH now that he's set up his team right in the sweet spot. Beyond that, the hated Twins have set themselves up to compete having made an excellent addition to a solid squad in JJ Hardy. Again eyeballing CHONE and ZiPS, the Twins are within striking distance, largely canceling out the Sox' advantage in the rotation with Mauer and friends. As it stands, the Twins have a distinct advantage at DH in Jason Kubel, whom ZiPS and CHONE see as worth a very average 2 wins, which Cust or Thome could certainly take back.
[updated to include the following - colin]
5) Asinine Speculation About Prospects
It's always hazardous to guess at Kenny's thoughts, but...let's at least brush up on what kind of prospect package he'd be willing to put together. The only way to make it really count would be to include either or both of Tyler Flowers and Dan Hudson. The team seems to have treated Flowers and Hudson as pieces of the puzzle in turning this core into a long term contender. Hudson appears to be DJ Carrasco's replacement until he proves he's better than Freddy Garcia, which is a nice way of getting Hudson consistent low leverage multiple inning work and making sure Freddy stays focused on keeping his job.
For Flowers, the assumption is apparently that he has the backup backstop spot on lockdown. When I squint, I see where Kenny's going with it: it's a cheap stopgap that turns into a carrot for Flowers and puts him in a position to succeed in a platoon with AJ. His high K rate is going to bother him the most early on, so ABs against lefties will ease him in. But what really matters is him sticking as a defender. CHONE and ZiPS have him as better than 1 WAR per 150 games as long as his defense isn't atrocious. If that's the case, then it's a possibility Kenny, giving Flowers spring training and the first third of the season to show he's ready with the bat, flips AJ before he gains 5 and 10 rights. Of course since there is something to gain from bluffing that The Boogeyman might be that ready, it's not necessarily the case that Kenny's credible here. The conventional wisdom is to make sure your prospects get as many reps as possible.