Nava especially deserves note as he goes under-appreciated far too often around here. Despite the slow start he finished with a wRC+ of 118 against RHP. From June to September he didn't have a single month below 100, with a June > Sept. of 122, 126, 101, 134 (he got roughly 15-20 more PAs in August than the other months, suggesting he saw more LHP in that month as well).
So knowing that Daniel Nava is a well above average hitter with a high OBP (getting almost as rare as power in MLB today) and improved his fielding last year, why take him out of the lineup? Despite his slow start he finished 2014 with a higher wRC+ against RHP than Cespedes (118 v. 117), who had a significant reverse split last year.
Daniel Nava is a good heavy side of a corner OF platoon. They just need to stop letting him ever face LHP. You do that by having both Allen Craig and Shane Victorino on the roster looking for platoon ABs and Brentz in AAA as the fallback platoon partner should one/both of them get hurt/fail to produce.