Dickey starts were the only reason to watch the team after the all star break, and I hate to see him go from a sentimental standpoint. But, he's 38, knucklers are notoriously inconsistent, and the Mets aren't built to win in the next year or two. I'll take a top flight catching prospect.
D'Arnaud has some pretty big question marks around his knee, though. If he has to move to first base or a corner outfield spot, his prospect value takes a pretty big hit.