Both are definitely important. The theming of Carsland is Disney's best in quite a while, in my opinion. On the other hand, like you said, DCA needed a new E-ticket attraction, and not only is Radiator Spring Racers one of those, but it's also one of the best rides Disney has built in decades. But yeah, it does help that Cars has a lot of appeal among children, despite of being one of Pixar's weakest works. In regards of which land seems more feasible, I think that Star Wars has a bigger chance than Cars. Carsland has become DCA's golden ticket, and I feel like the company wants it to remain a DCA exclusive. I think that an expansion of Pixarland is even more possible than the creation of a brand new Carsland. And Frozen land, yeah, I don't think that's ever happening.