My points

If a manager really determinates promotion based on employees' appearances, s/he is not a good one and does not know how to use the talents.

I think the safest way is dressing a little higher than your coworkers but never overdo, never exceed your female boss. Dressing up too much makes yourself unapproachable and you may look like a snob. Others may think you are tardy and unprofessional if you dress down too much.