Is it permissible for a man to use a hairdryer to improve the appearance of his hair, without exaggeration or imitating women or disbelievers?

If your action does not involve imitating disbelievers, transgressors, or women, then there is no harm in it, because the default rule is permissibility. The criterion for thehibited imitation is that which is exclusive to one of the genders, so it is not permissible for the other to imitate it.