I'm a little late to this as I've been touring the holiday travel delay circuit. But, I have to say, I wasn't exactly "amped" when I heard about this trade - one that could potentially become harder to defend if the two prospects are revealed to be more than roster-filler. Sean Marshall is a reliever with one year before free agency, while Travis Wood is a starting pitcher with 5 years of team control who - as recent as last year - was getting everyone all excited as a potential rotation fixture.
The best thing to recommend it is that it's an all-in move. If it wasn't abundantly clear before, eliminating roster redundancy and playing for next season is Walt's MO this winter. This deal undoubtedly makes the Reds better in 2012, as they needed a top-flight reliever AND a second lefty in the bullpen, while Wood was on the outside looking in to the rotation. Depending on whether you weight next season's playoff hopes above all else, this trade could easily be spun as a winner.
Of course, evaluating the players involved is essential to forming an opinion about this trade, regardless of whether you're more into years of control vs. 2012 success. A closer look at Marshall reveals that he's much more than just a second banana to Bill Bray in the bullpen (bang). He started his first two seasons in the bigs and has both shown durability while, judging by his 2010-11, just hitting his prime years. He's been an elite, closer-caliber reliever during the last two seasons who, while better against lefties, has nice-looking splits against righties too. And even though Marshall is a free agent in 2013, he's a good candidate to be a ranked by Elias (UPDATE: this doesn't exist anymore, but Marshall could still be a top free agent under the new CBA) and be offered arbitration - so the Reds could get Marshall back or a 2013 first-round pick out of the bargain.
Wood, entering his age 25 season, has plenty of room to grow into his minor league line. He's been impressive both in the minors (PitcherOY in 2010) and during the first half of his 2010 debut , but was eminently hittable last season. With a fastball that averages 89-90 and some scouting opinion that put him in the 5th starter/journeyman range, the brain trust may have seen something that wasn't fixable for Wood's future as a major league starter.
I don't like giving up 5 years for one, especially since I thought Wood had a role to play next season and would see some kind of bounce-back, but I see a lot of virtue in Walt's strategy to take the org's best players who were either blocked or on the margins on the 25-man roster and turn them into a major upgrade of the pitching staff.