Training the decline press might be good for some variety. Beyond that, I don't see what they offer over what that the flat variety does.
I don't buy into the whole thought that you can target certain parts of your chest with different angles of bench pressing. Certainly some exercises will target the chest as a whole more than others, but not certain areas.
I also agree that Dips are a great movement and target the chest, shoulders and triceps equally as well as the bench press. Dips can also give you a greater range of motion over the decline press.