The Dapper Day website is pretty clear that you don't need to attend the expo to get the discounted hotel rate. Dressing up for the parks on April 19
is participating in Dapper Day and qualifies you for the rate. And Disney is the one providing the discounted rate (it's not like the Dapper Day organizers subsidize it), and Disney's interest is in promoting the parks, not in what's going on in the convention center.
So,
@Captainkidd76, if you want to go to the expo for a day, that's great. But if you and your family would rather be in the parks, then do that and don't let anyone tell you you're abusing anything. If you're in the parks, you're actually supporting the organization that
gave you the discount (in this case, Disney). Don't force your kids to go to the expo, and don't get bullied into buying expo tickets because they're "only $15" (each).