Even if the air stayed a perfect insulator your hair would be attracted to a positively charged VdG dome.
The VdG dome produces an electric field which would produce a separation of charges with your hair having a net negative charge and parts of you body and the Earth having a net positive charge.
Because of the repulsion between the strands of hair it would probably also stand on end.
The distribution of the induced negative charges on the hair would not be uniform with the greatest surface charge density being at the most "pointed" parts of the hair - at the ends.
This large surface charge density would produce a large electric field in the air surrounding the hair.
If the electric field is large enough ions and electrons will be produced and hence in effect the air will become a conductor which is called action at points.
The electrons will be repelled by the hair and move towards the positively charged VdG thus discharging it and at the same time you are "gaining" positive charge.
The reason for the spherical dome on the VdG is to have an object without any points, edges etc so that the electric field at the surface of the dome is kept to a minimum.
Dust on the dome or dents can reduce its effectiveness in terms of storing charge.