Well, you are the expert on aviation. You know more than those in the industry. ;) I'm sure that they have performed studies to determine customer values. Is the extra .5 inches worth it??? I've been on a 757 the last few flights I've flown. I would not be impressed with an extra half inch. How about you?
The standard 757 seat is 17.2 inches, and the 747 seat is 17.5 inches. If you added 0.5 inches to the to the current 747 seats, they would be the same width as seats used on 767 and 777 depending on the airline. That's 0.8 inches wider than a standard 757 seat. Consider that the 787 will have a 19 inch seat width, and the A380 will have 18.5 inches. The 747-8I might be flying SYD-DFW. Having a little more room would be a serious improvement in comfort. If you notice the difference between the seats on a 767 and a 757, you'd probably also notice the difference if the 747 cabin were upgraded.