I had a 04 and an 05 at the same time, an someone said just what you do so I wnt and looked closely and unfortunately I could not see any real difference. You may be right but side bu side I could not see it.
Basically what the dumb key fob does PLUS. Allows you to open doors by pressing the button on the door and start the car by twisting the know on the dash without putting in the key. So cary the new fob and eliminate some hassle.
Actually it's kind of nice not to have to drag out the keys. As long as they are in your pocket, the vehicle will open, turn on, etc. Only realy problem is when the battery runs out (nissan says 8-9 months battery life). Life is tough. <grin>