I dug into his splits a bit, wondering if he's unlocked something. And the answer is... maybe? He basically hasn't walked since the all-star break - his batting average has gone up by 49 points in H2 vs H1, but his OBP is DOWN 7 points. That seems hard to do. SLG up by 19 points.
Over the last month, though, he's at .299/.322/.460, which is fine. .313/.327/.542 over the last 2 weeks. If he gets that OBP up he'll be a nice low-mid .800s OPS guy, which I think will put him over 2 WAR as a first baseman over a full season. He's probably never going to be more than mid-high 4s SLG, though, unless he earns more power through being more selective or through a swing improvement. I doubt the Sox can do either.