Your headshots are the first mode of communication an agency have and they should be appropriate enough to make an impression and force the agency to have a conversation with you. You do not need to have your portfolio taken by Steven Meisel by spending lots of bucks but they should definitely be professional enough to give the agencies insight that you actually want to be something.
In other words, your photos should be well groomed, posed with confidence with minimal make up that defines your natural beauty and should be current. Making a first impression is very important in the glamour world and you should be careful enough with that if you need to be recognised.