The Sox offered two deals to Minny last winter:
1) Ellsbury, Lowrie and Masterson for Santana
2) Lester, Crisp, Lowrie and Masterson for Santana
Clay was deemed an untouchable at the time. The Twins were holding out for both Lester and ellsbury. The Sox obviously at the time ranked Clay ahead of ellsbury and Ellsbury ahead of Lester. Just b/c Lester, Lowrie and Masterson are doing better this Summer than Clay and ellsbury doesn't mean we should give up on either of those 2 guys. There were many times it seemed like you could say it was time to give up on Lester in the past and now he's become one of the finest young pitchers (AL Pitcher of the Month for July. First sox winner since Pedro in '02).
In hindsight, The Twins have to be kicking themselves for not taking option #2 and we have to consider ourselves very lucky to have Lester, Lowrie, and Masterson making next to nothing on our team and 20 mil extra in cash to play with.
I do question a little the Sox evaluation of their prospects. They deemed Clay untouchable, but were willing to trade Lester. They were willing to throw in Masterson and Lowrie. They thought Hanley wouldn't cut it in the majors (yes Beckett was a great pickup, but the point is the top baseball FO's do a better job knowing what prospects to keep and what ones to trade. Think the braves). Murphy was deemed by Boston to be a career backup and has done well in Texas. The other guy they traded in that Gagne trade, Beltre, is considered one of the top young prospects in the minors. I'm also scared that Moss might end up being a very good outfielder. The Sox also drafted one of the best slugger prospects, LaPorta, a few yrs ago, but didn't project him well enough to pay him enough over slot to sign him (we're talking minimal money here for a team that can kick in 7 mil to have another team take on Manny).
So in retrospect Santana would have been nice to have, but we are really lucky that Minny didn't take the Lester, Crisp, Masterson, Lowrie offer. If the OP meant we should of traded Ellsbury and Clay for Santana well that's what the Twins originally wanted and they would have taken that in a heartbeat. Too early to tell if we made a mistake, but I think that Clay and ellsbury's stock have dropped a lot since the winter and it would be a terrible mistake to give up on them now, when their stocks are low. I think ellsbury is a little injured and the Sox made some silly adjustments to Clay's delivery which has messed him up (they did the same thing to craig Hanson yrs ago after he was basically unhittable and he's never recovered).