Yes, 1080p is A HUGE upgrade from 720p.
If you have a PC with a 1080p capable screen, go watch a youtube video at 720p and fullscreen it, then go watch the same one at 1080p and fullscreen it. There's your answer.
720p = 921,600 pixels
900p = 1,296,000
1080p = 2,073,600 pixels
If you don't notice the difference, then I recommend seeing an optometrist. (eye doctor) and getting some glasses or contacts.