The Gronk situation makes things tough. Bennett was idea because he presented a legitimate second threat, but also was good enough to take over the 1 spot. Finding a guy who can be effective along side Gronk but can also take his place is a very tall order. There were reasons to believe on paper for example that Chandler could be that guy but that didn't turn out so well. Bennett is due a good signing bonus and a three or four year contract with at least half guaranteed. Not really in the cards for the Patriots. (Speaking of Cards, that is my guess for Bennett.). Take the comp pick, and just be content with having found the right guy in a Super Bowl year who cost you nothing more, really, Than some bucks you had to spend and likely will secure a comp pick to feel better about giving up the fourth rounder to get him.
Not a lot out there in free agency to be Gronk insurance. Doyle, Luke Wilson. Maybe you take a look at a guy like Gresham. You hope maybe Brady finds something Carson Palmer couldn't, and if not at least you have a great blocker. The kid behind Ertz in Philly is supposed to be pretty good. I think he's an RFA. Mychal Rivera in Oakland has had some good games.
Or maybe you throw some money at Vernon Davis for a year. He just spent a year behind a non-durable, elite tight end, and he also knows how to take the 1 role if he has to.