For a football team, 72 million dollars is far easier to replace than 2 first round picks.
It's only a 1 and 4 if they miss the playoffs. It's two 1s if they win the SB. There's three ways to view that trade
1) In the abstract, is Sam Bradford worth a 1st and 3rd round pick? Most would say no
2) If you knew that the Vikings were going to be playing 3rd string tackles, backup center, a backup guard, miss Peterson for most of the year, miss Diggs for a couple of games, and get nothing from 1st round WR Treadwell, would you make the trade? Obviously not. You'd trade away every player you could in the face of a lost season
3) In August, after losing Bridgewater, but expecting league average injuries, and expecting the young defense to be special, would you make the trade? To me, this is the proper way to view the trade when evaluating the job Speilman has done