I'd like Joe to be less selective but in my view his failure to adapt his approach isn't nearly as big of an issue as his failure to adapt his swing.
While everyone else in the league has now realized the benefits of trying to get lift on the ball, Mauer is still trying to swing across a table top. More importantly, there's a reason he's not hitting lefties like he used to, he's having a harder time catching up to them because, duh, he's 34 now. He always used to get complemented on how he was able to wait on the pitch and hit it towards the back of the plate; he just can't do that like he used to. There's a reason so many of history's great hitters developed more power but struck out more toward the end of their careers; they'd start cheating on pitches.
Like so many others, Joe just has to suck it up and realize that change isn't shameful but necessary. 34-year-old Joe Mauer should not have the same swing as 24-year-old Joe Mauer.