After days of rumors and speculation, the Giants have finally acquired outfielder Hunter Pence. Heading to Philadelphia are Nate Schierholtz and a pair of prospects — Tommy Joseph and Seth Rosin. Hunter Pence, 29, is under team control through the end of 2013, but is set to make nearly $15M next season.

The Giants certainly improved today, but Pence isn’t some kind of big upgrade. He’s having somewhat of a down season, hitting .271/.336/.447 (111 wRC+), and yet that’s not much worse than what he’s done over his career: .290/.342/.481, 118 wRC+. The safe bet is that he’ll continue to perform as he has so far this season, providing good — not great — production at the plate. And that’s ignoring his defensive skills, which have rapidly faded. All of the defensive metrics (UZR, DRS, FRAA) seem to agree that he’s a mediocre fielder at this point (and with Angel Pagan patrolling center field, that’s cause for concern).

Even in spite of his recent struggles, Gregor Blanco has been average with the bat (101 wRC+) and spectacular with the glove this season. So it’s not as though Pence is filling a major void here. He’s an upgrade — make no mistake — but not a significant one.

Yesterday, I tweeted the following:

Justin Christian batting with two outs in the ninth inning of a tied game is why the Giants could use an outfield acquisition.

— Giants Nirvana (@GiantsNirvana) July 31, 2012

And that’s where the impact of this sort of deal can be felt. The one thing I was hoping the Giants would accomplish in trading for an outfielder: push Justin Christian off the roster. Even if Pence wouldn’t be much of an upgrade over Blanco, the Giants would have a markedly better bench with Blanco taking over Justin Christian’s spot. With Nate Schierholtz gone though, that unfortunately won’t be the case. Nate probably isn’t an everyday caliber player, but he’s a very good fourth outfielder: he’s held his own against righties and lefties throughout his career (94 wRC+ and 95 wRC+, respectively), he can handle right field at AT&T Park like so few others, and he’s a good late-inning pinch running option. So it’s easy to downplay what the Giants gave up in Schierholtz, especially considering that he’s still under team control for another couple years after this.

As for Tommy Joseph, the centerpiece of this trade, I’ve always been relatively low on him as a prospect; one of the main reasons I wasn’t too optimistic about Joseph was his defense, something that is of paramount importance when it comes to catchers. But he’s reportedly shown dramatic improvement in that regard. And, of course, that power-heavy bat is what makes him special: he’s put up league-average numbers in Double-A Richmond as a 21-year-old catcher — quite the promising sign. From the Giants’ standpoint, they can afford to give up catching depth with Buster Posey, Hector Sanchez, and Andrew Susac already in the organization, but as an advanced hitter at the most demanding position in baseball, Joseph is a pretty valuable piece. As John Sickels put it: “Joseph isn’t a sure thing by any means and catchers often have unusual development curves, but there aren’t that many potential regular catchers in the minors.”

The final piece headed to Philadelphia, Seth Rosin, could pan out as a solid middle reliever. The 23-year-old pitcher has put up strong peripherals in High-A this season, although he’s a little old for his level.

Ultimately, at the risk of this seeming like a cop-out, I’m neutral on the deal. The Giants acquired an above-average outfielder, and he’s not just a rental. But their starting lineup only got slightly better, and the deal comes at a considerable expense: the three players headed east, as well as the money owed to Pence throughout the next season and a half.