It is difficult to admit failure--but it is inevitable. The question is: do it in Spring training or wait until May/June? The write-up on these guys was oh so kind. "While no one thinks or expects to put up the numbers in 2014...". Since he isn't an OF ("...Hunter will spend a lot of time...") and now it is accepted he won't hit much--he should receive a spot on the active roster? At 25 he is no kid--and his ceiling is as a bench player who isn't much defensively and can't hit--why keep him? There are many better options on the team.
Arcia--he can't play either corner--he can only be inserted there (like Willingham was) and hope they don't hit the ball his way. "He catches most of what he gets to..."--so do little league kids. As a hitter, he "disappoints" (to be gentle) and quite frankly there are many better options in the minor leagues for the OF.
Tonkin--relief pitchers cycle in performance frequently. If he has a strong Spring--keep him. Else, cut him loose, there are lots of good candidates in the system.
In short, very little time should be spent on bench players. If they don't quickly succeed--cut them!
If we followed this advice there would be no Michael Cuddyer, no Aaron Hicks, no Trevor Plouffe. Guys develop late (see Dozier, Brian) and you can lose a ton of value by cutting people too quickly.
The Twins shouldn't be blocking anyone to keep these guys but that's not really the case. Tonkin is a good a bet as anyone in the pen, Santana is your best utility guy and Arcia doesn't block anyone (you can have Buxton, Roasario and Sano all playing with Kepler developing in AAA and Santana as a late inning defensive sub for Sano.) In no case is keeping these three something that stops other guys who deserve it.