A moderator or trusted user should be given right to straight away delete duplicate questions with answers that won't change over time, as they would already have enough experience to understand which questions differ from each other. The user can then be given option to edit the question or remove it if he thinks its duplicate too.
Moderators already have the ability to do this as well as merge duplicate questions, although it is never really necessary. Trusted users should not have this ability, usually duplicate questions serve as signposts which direct users to a canonical answer. We shouldn't be promoting their deletion by suddenly allowing trusted users to delete them.
Also keep in mind that sometimes people answer duplicate questions many years after the original with more up to date code, which we have to account for.