If you hypothetically trade Miggy and Trout, which team improves? I would argue its the Angels, who have Bourjos who can step in and play the outfield above replacement level, whereas the Tigers have no clear options at third that are decent since they moved Castellanos to the outfield. Ramon Santiago? Andy Dirks? Plus either Trout or Jackson would take a hit on value, moving to left field, in terms of WAR. (+2.5 runs for CF to -7.5 for LF)
Therefore I would argue Miguel Cabrera, in the context of 2013, is the more valuable player.
Disclaimer: I understand you can't do this hypothetical swap with every team. You can't, for example, swap Jose Altuve and Trout (or Cabrera) and wonder which team will improve more.