Most of us have been pleasantly surprised by Pedro Alvarez' defense at third. Not that he's been a stud, but UZR/150 has him just a bit worse than 12 runs below average. SSS and all that, but it tracks what we've seen: a guy with poor range, but otherwise decent fundamentals.
But let's look at the bigger picture. Pedro figures to be somewhere around .385 wOBA (hopefully a bit more, but let's not be greedy), and if his defense continues at this level, that's around 44 RAR, or 4.5 WAR (+32 batting runs, -12 defensive runs, +22 replacement runs, +2 positional). Not bad, but not thrilling.
Meanwhile, over at 1B, we've got GFJones, performing adequately but below par; even if he heats up, he'll end the season below 2 WAR (assuming he doesn't go crazy again, that is). Pedro, hitting the same and defending a bit better at 1B, profiles around the same as at 3B, perhaps a hair better; we'll call it 4.5 WAR (+32 batting runs, 0 defensive runs, + 22 replacement runs, -10 positional).
So who plays 3B? Why, Andy LaRoche, of course! Would this make sense? Well, if he merely duplicated his 2009 performance, which was worth 2.6 WAR, we come out perhaps an entire win ahead relative to the status quo.
The two big questions marks are whether Andy can return to (or exceed) his 2009 form, and whether Jones (or anyone else) can get you better than 2.6 WAR at 1B while leaving Pedro be. Because my biggest concern would be moving Pedro for Andy, then having Andy fail, and moving Pedro back - that's not a great way to treat your best player.