Vimd is your min drag speed (indicated). It is used in Range and Endurence calculations, not Take Off performance calculations. With referance to the take off you would have to compare Vimd to Vr to see what the effect eould be. If it was the same then there would no effect. If it were lower and you tried to unstick there would be a chance the a/c wouldn't fly. (Weight would exceed Lift). If it were faster the story becomes a little more complex but this has nothing to do with the question.