Only one slight quibble with your napkin math is we don't know their actual costs for food, labor, etc. Some here can help us get that but you're giving them a full profit which isn't entirely fair. Again, not "Grading" just pointing out it won't be quite as much in the house's favor as your napkin math suggests. It'll still be quite nice but they can't hold onto all of that money, they still must pay the line items first. The real bonus is if they are able to increase the table turnover, which might make the (good) waitstaff happy.
As for the other get an autograph the first time and after that we just snap a photo, do a hug/high fives just to keep our time spent minimal. That being said, I feel for parents with young ones who believe in the characters. I like the autograph card and would also ask for two to display front and back. At least it isn't a plain index card!