Two words came to my mind when I saw this headline on MLB.com - Ricky Weeks. I dug out an old spreadsheet that I have that does "rough" MLEs, looked up some park factors, and did a quick MLE.
2005 Spivey: .236/.308/.374
2005 Weeks MLE: .289/.360/.496
I would really like a better way to do MLEs, but a lot of the data for them is proprietary from various sources online. So use these MLEs with caution.
I can provide some hard data, though, from milb.com: Weeks is hitting .320/.435/.655 in AAA-Nashville. That's exceptional, even in the PCL (and Nashville has a reputation as a pitcher's park).
Weeks will almost certainly be an upgrade over Spivey for the Brewers, assuming that they plan to call him up.
The rest of the deal, then, is a bit less important, but they did net a pitcher that I like a bit: Tomo Ohka.
The unheralded Ohka has never been a star, but he has a career ERA of 3.88. Ohka's 3.33 ERA this year is extraordinarily deceptive, though; his control, which is always pretty solid, has been nonexistent, and his strikeout rate is actually lower than his 3.33 ERA at 2.83. That's lower than it will be at the end of the year, but Ohka is the beneficiary of a .212 BABIP, which is the source of, basically, everything, for Tomo.
Ohka's 2003 is about where I think his norm is:
199 IP, 233 H, 92 ER, 24 HR, 45 BB, 118 K, 4.18 ERA
Ohka's not a great pitcher, nor a particularly good one, but he fits a mold that Prospectus frequently lauds - an average pitcher that can give you 200 average innings. That's a plus, IMO, and, considering that they gave up Spivey, that's a great pickup for the Brew Crew.
The Nationals are banking on Spivey returning to his more typical career stats rather than his abysmal '05; he's a career .272/.355/.438 hitter, which is valuable in its own right. He'll be Vidro's fill-in until the All-Star break, which is much further away than you'd think, and, assuming he rebounds from the early season slump and recovers, he'll be a solid fill-in.
I like what the Brewers got in this a lot, but that's mainly because of the fact that it was time to get Weeks into the lineup. Hopefully, they agree.