I've been to the event 3 times with Icons with 21, 25, and 26. I'll say that with 25, yes, it absolutely made a difference. With Jack's show, the background music throughout the parks featuring snippets of Jack, and the like, it gave the event a cohesive, unifying experience.
Lady Luck and Chance, however, did no such thing.
So I'll say that when an icon is done right, yes, it absolutely makes a huge difference, IMO.