Not having to install any sound deadening is really the purpose of the mass backing. That being said, you could install more, with spray-on types (like Lizard Skin, Second Skin, etc. being the least obstructive) or maybe a thin asphaltic material (like a 50mil KillMat, Noico, etc.) The mass backed material is already thick, and you don't want additional thickness to create fitment issues (like where the carpet fits into the cargo area panels, thickness under the seat mounts, etc.) Where you CAN see some benefits in addition to the mass backing is to apply some thicker material (80+mil asphaltic material) to the inside of the exterior door skins and quarter panels.
I installed mass backed carpet in my 2000 100, and it made a pretty profound difference. I suspect the difference isn't quite as pronounced in the 2003-2007 trucks, as they got more sound deadening from the factory than the 1998-2002 trucks did.