You have to aim for both demos. Somehow Disney is able to do it, so it's not impossible.Universals' main demo is millennial...
While families are great, you don't at the same time dismiss your key demo for another demo.
Universal is opening a lot of hotel rooms within the next year or so with Aventura and the W&W hotels (and then eventually hotels at Site B). Who's gonna pay to stay there and keep those rooms occupied? Sure some will be millenials, but you NEED families too or you won't be able to keep a high occupancy.
It also affects the per guests spending. Families and older folk who tour the parks who have money to blow don't really care if some things are over priced. The younger demographic (which i'm a part of) is very cautious with their money.