I understand that, and with the Dolphins in rebuilding mode, that's the reason they should trade him. But he's a first-team All-Pro with a relatively low cap hit, so there is going to be competition for him and Miami is going to want to get as much as possible.
I think we always want Dallas to win trades with the least amount of compensation possible, but I don't think we're always realistic on value. It's like some thinking the Raiders wouldn't be able to get two first-round picks for Crosby (although I guess ultimately they didn't because of the medicals).