With 13 position players there is a way to do this. Mastro and Komatsu are not top 30-40 (or more) prospects, so they can stay and fill-in in marginal roles (and probably do well in those roles--Mastro, albeit in a worthless game, just made a great play in LF). Hell that was, one would have thought, the reason for Mastro's signing in the first place. Anyway, if Morneau can play first a bit more, they can DH Willingham twice a week, spell Span one game one week, Willingham the next, and let Ben get one start in RF as well once a week. That way he starts 4 games and Span, Willingham, and others get rested. The same applies for Plouffe--play about 4 games a week. I think it is go time for these two. I am sure Revere will be fine, and Plouffe's four homers and plenty of walks are helpful for his cause. Plouffe and Mastroianni also provide emergency backups in the middle infield. If Plouffe fails, then Valencia can return. If he doesn't, then they have to figure out which one brings the most value in a trade (I know it won't be much, but perhaps a more or less major league ready Plouffe or Valencia garners an A ball pitcher with some good velocity--something).
I am pretty pleased with the current makeup of the Twins roster in terms of position players (ride the Butera train until it "Mendozas").
The pitching staff, on the other hand, is in need of further changes. DeVries and Walters are likely not really good replacements, but worth it for now. I think Bromberg might be working his way for a shot this year, which is damn good for the poor guy.