You can't keep non-productive guys on your team because you are afraid if you cut or trade them, they will help someone else. You would end up with a squad of non-performers.
It isn't what you can get vs what you give back. It is do you want the guy on your team or not. That is the questoin that counts. If you want him on the team, keep him. If you don't want him, you cut or trade him, and it is hard to say that cutting is better than trading unless you are sending a message to the team. Usually getting a fifth, sixth or seventh rounder is better than not getting one.
People think late round picks are worthless when we trade for them (WE gave up Play X for a lousy end-of-the-draft pick?) yet go beserk when we trade one away (we gave up a draft pick for that waste Player Y?)
Personally, I hope Galloway works out. I like him. But if it is keeping him inactive for the next 10 games and the playoffs vs taking a flyer on someone else, then I'd go with the flyer.