The two areas that need the most help are hitting and pitching.
Hitting: Jorge Polanco and Oswaldo Arcia. Put them in and play them for the rest of the season. They're both supposed to have good bats; Polanco is supposed to be a decent SS, and Arcia needs work at corner OF, but can DH and PH. Plus, Arcia is the best bat in the Twins system to sit behind Sano against rightie pitchers.
Pitching: We all agree that Blaine Boyer isn't getting it done anymore, and Duensing hasn't looked much better. Replace them with Jose Berrios and Taylor Rogers. Extended looks for both, no matter what (throwing in the towel).
Beyond that, other promotions and shuffling should favor just the younger, more promising players, not more shuffling of veteran retreads. I'd get Max Kepler to AAA right now, working on OF and 1B, then look at a September call-up. It's still too hard to imagine moving Joe Mauer to the bench, but at some point you've got to get more power at 1B.
I would also move batting coach Tommy Watkins to AA Chattanooga. He was the last coach that had Adam Brett Walker's K rate at 20 percent. Whatever he was doing worked much better that what Chad Allen is doing. Results have to count for coaches, too.
I think it's obvious at least defensively Polonco isn't ready yet. I can see him up in September, but I'm guessing for now they want to give him everyday reps while they can. I think almost everyone would like to see Arcia up in platoon against RHP and PH situations and I believe it will come, but right now they feel content on giving him everyday AB's, but I wouldn't be surprised to see him sooner than later.
I would assume it would be pretty low chance we see Berrios before September. IMO, having him keep starting in AAA, where he has only been a short time, is better than him in the pen pitching a handful of innings per week. There are several candidates that IMO should have replaced Boyer months ago.