After trading away those expensive players, your next two seasons will have a significant amount of dead cap space. Keep in mind, if you don't get under the cap, your coaches will cut the most expensive players before your first game (I can't remember if it's the first pre-season game or the first regular season game).
By trading them away, you can get something out of them. Whether you trade them or not, your dead cap will still be effected. There's no getting around that.