I think Slow Pitch is right.
It's important to distinguish between two things:
1. Did the Red Sox get a fair return for Nomar?
2. Did the Red Sox improve their team in this trade?
Slow Pitch didn't say anything about #1. Could the Sox have used another pitcher? Absolutely. Would Clement have been a nice addition to BOS? Of course!
But let's leave that aside. What about #2? Did the Red Sox improve themselves?
I think they did, and for the reasons Slow Pitch mentioned (give or take). They get a nice defensive upgrade in the IF. I find it difficult to assess defensive ability, but from most accounts Cabrera is a very good defensive SS, whereas Nomar is an average-to-good defensive SS. Mientkiewicz is a huge defensive upgrade at 1B.
This does force the Sox to play Millar in the OF, and relegates Ortiz to the DH. This also means that Manny won't see the DH much at all. But Roberts isn't a bad addition. It's a bit strange, but it does add depth to their bench. He can be a defensive replacement, in the right situation, and can be used as a pinch-runner or sparkplug when they need speed on the basepaths.
There's something else to notice, a larger trend. Beane made moves in the off-season to upgrade the A's defense (contrary to the Moneyball storyline). Now we see another sabre-guy in Theo moving to upgrade his slugging team's defense. Is this a coincidence? Or have these guys been re-evaluating defense in their grand schemes? Something to consider ... and to watch for again in the off-season.
"The game has a cleanness. If you do a good job, the numbers say so. You don't have to ask anyone or play politics. You don't have to wait for the reviews." - Sandy Koufax