That's not at all what I'm saying. The "extra year of Berrios" means two things, not one thing, as you believe.
1. He gets to pitch for the team for a longer period of time, if they want him to. But remember, the goal would be, unequivocally, for him to help them make the playoffs this year.
2. The team gets to trade him before he hits free agency. This is great, too, especially if they traded for him in the first place.
The team could trade him at the end of the season, or the team could trade him at next year's trade deadline. But make no bones about it, he is very likely to be traded again.
Get it now? Berrios's "extra value to trade this year" is because the acquiring team can trade him again, and thus the second team can come out ahead. With Berrios's production just below that of ace, he will always get a good return on the market.
This is a bad idea, and hopefully the Twins are not entertaining it. Let the fans and the bloggers think about it all they want. The universe has tons of space with which to fill up chatter, after all, and there are worse options of things to talk about.