First, there's the question of where he would play. It's an obvious one, but why trade for a player at a position that is pretty much filled? Is there some thing we're missing about our corner outfielders?
Yes, Jason Bay hasn't been good. He hasn't managed to be above average in two years now. If he can't manage to be an average defender in the corner outfield, he is not a candidate for center field.
If the team is treating him as a sunk cost and is ready to move on, then perhaps it would make sense to get a young, cost-controlled corner outfielder for the future. Lucas Duda can barely play his corner outfield position, he couldn't handle both corners. Brandon Nimmo is the big hope for center field, and the last big hope for center field, Kirk Nieuwenhuis, doesn't look like he has a bat for the corners. At least not while he's striking out more than a quarter of the time. Cesar Puello is in high-A ball and can't take a walk. Maybe there's a need here.
Is Smith the one to fill it?By most measures, Smith has been above-average with the bat in every year in the bigs -- but not all. Once you weight his runs created and take his home ballpark into account, his 2010 was below average (98 wRC+). And while the rest of his ledger shows offense that's 10% above league average, the package doesn't come without flaws.
Smith has a heavy platoon split. His wRC+ against righties is 125. Against lefties, that number plummets to 47. It's only come in 239 plate appearances, and typically you'd want to regress that split towards the league average until he's accrued about 1000 PAs against both hands. But! Couldn't we add in the 300 or so PAs in the high minor leagues where he was bad against southpaws too? He didn't once slug above .400 against lefties above High-A ball.
So he's about three-quarters of a quality bat. His defense in left field is about scratch -- 1.4 UZR/150 over 2569 innings -- so he's not going to be a plus or a minus with the glove.
That's why he's spent the last two years being almost perfectly average (3.4 WAR over two years, 2 WAR is about average).
He walks at an average rate (8.6% last year, 8.1% was average). He strikes out at an average rate (17.4%, 18.6% was average). He reaches a little more than the average rate (32.2% O-Swing %, 30.6% was average). He makes contact slightly less than average (78.5%, 80.7% was average). He's stolen some bases, but his career speed score (5.8) is just above average (5.0), and Bill James projects him to be average with the wheels next year. Whatever pop he has (.200 ISO last year, .144 was average) he gives back with the platoon split on some level. It's, you know, average.
At 29 years old, he's not about to get better. In fact, his best days are probably behind him. If he was a scratch defender, bad defense could be on the way. If the wheels erode, and the contact skills slip just a little bit, he will fail to be any better than an average player for the third straight year in 2012.
An average player has value, especially when you're unsure you can field an average corner bat with the options at hand. But Smith is also entering his final three arbitration seasons, and he puts up the good batting averages that arbitrators like. He's slated to make just short of three million dollars this year, and his value last year by WAR was just under ten million dollars. By 2013, he won't be much of a bargain any more, and the other Mets outfielders will be close to the majors.
Seth Smith is okay. Average even. But, unless he's paired with Wilin Rosario, and probably a pitching prospect, he isn't a great trade target for the Mets. Even then, if the pitching prospect could be better if the Mets didn't take Smith, that would be a better idea.
Two years ago, Jason Bay had a terrible season. He was worth .2 WAR less than Smith. Last year, Jason Bay had a terrible season, He was worth 1.2 WAR less than Smith. Is that win worth trading for?