Why do people underestimate Nani's value?

Because Nani is very dislikable. He's a horrific diver. In terms of value, Nani IMO is only slightly more valuable at the moment because of his assists. Sneijder over the course of his career has on average scored a hell of a lot more goals than Nani and has scored more for his national team on average as well. Sneijder's free kicks and passes are impossible as well as Nani's. Both brilliant players, but I think we have more to see of them because they're not as good as 'the highest level' as you stated. Looking forward to seeing more from both of them.